Re: [PATCH v5 27/28] ext4: xattr inode deduplication

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Thanks Andreas for the feedback. Please see my responses below:

> It would be preferable to allow a mount option like "no_mbcache" to disable
> the use of shared xattrs.  In the Lustre case at least, there will never be
> shared large xattrs, and we've had a bunch of performance issues with mbcache
> due to lock contention among many server threads doing concurrent lookups and
> inserting many thousands of unique entries into the cache.

I have put nombcache mount option in a separate patch ("[PATCH 32/32]
ext4: add nombcache mount option"). I have named it nombcache instead
of no_mbcache to be consistent with other no* options. Let me know if
you prefer no_mbcache as the option name.

> This should follow the existing convention of always using s_csum_seed to seed
> the checksum, and change ext4_fill_super() to initialize s_csum_seed to ~0 if
> ext4_has_metadata_csum() is false, or always use the same value regardless of
> whether ext4_has_metadata_csum() is set or not.

Done.

> If it really necessary to have more than 2^32 references on a single shared
> inode then it would be better to avoid the re-use of i_mtime, which breaks
> the backref for unshared xattrs, and using i_size isn't enough of a guarantee
> that this is the correct parent inode in case of on-disk corruption.

I have now moved the lower 32bits of ref count from i_mtime to l_i_version.

> Should this be contingent on ext4_has_metadata_csum() feature being enabled, or
> alternately check if EXT4_XATTR_INODE_GET_PARENT() and i_generation match before
> returning an error.  This will allow a smooth transition from existing filesystems
> that do not store the hash, but have only a single-use xattr inode with a parent
> backref.

I updated hash validation to fallback to parent backref check for
backward compatibility.

>> +     /* Indirection block. */
>> +     blocks += 1;
>
> Strictly speaking, this is only needed "if (blocks > EXT4_NDIR_BLOCKS)".

Ack. I didn't think it was worth going through exact calculation in
this case, let me know if you see value in doing that
I also updated the comment to mention extents.

>> +     /* We may need to clone the existing xattr block in which case we need
>> +      * to increment ref counts for existing ea_inodes referenced by it.
>> +      */
>
> Just to clarify here, in the case of cloning an existing xattr block, are the
> refcounts being _incremented_ or _decremented_ on the existing ea_inodes?  I'm
> trying to figure out if we really need to have credits for both old and new
> xattr inodes, as well as these additional credits.  Since this is reserving
> about 110 blocks for every setxattr, this can add significant pressure on the
> journal if there are lots of threads creating files and/or setting xattrs.

Cloning causes incrementing xattr inode references.

>> +ext4_xattr_inode_cache_find(struct inode *inode, const void *value,
>> +                         size_t value_len, u32 hash)
>> {
>> +     struct inode *ea_inode;
>> +     struct mb_cache_entry *ce;
>> +     struct mb_cache *ea_inode_cache = EA_INODE_CACHE(inode);
>> +     void *ea_data = NULL;
>>       int err;
>
> This function should just return NULL if ea_inode_cache is NULL (e.g. in
> the case of "no_mbcache" mount option).

Done in later patch ("[PATCH 32/32] ext4: add nombcache mount option")

> Should skip mb_cache if EA_INODE_CACHE(inode) is NULL, or have a wrapper
> like ext4_xattr_inode_cache_insert() to match ext4_xattr_inode_cache_find()
> that does the same.

Added skip in patch ("[PATCH 32/32] ext4: add nombcache mount option")



On Tue, Jun 20, 2017 at 2:07 AM, Tahsin Erdogan <tahsin@xxxxxxxxxx> wrote:
> Ext4 now supports xattr values that are up to 64k in size (vfs limit).
> Large xattr values are stored in external inodes each one holding a
> single value. Once written the data blocks of these inodes are immutable.
>
> The real world use cases are expected to have a lot of value duplication
> such as inherited acls etc. To reduce data duplication on disk, this patch
> implements a deduplicator that allows sharing of xattr inodes.
>
> The deduplication is based on an in-memory hash lookup that is a best
> effort sharing scheme. When a xattr inode is read from disk (i.e.
> getxattr() call), its crc32c hash is added to a hash table. Before
> creating a new xattr inode for a value being set, the hash table is
> checked to see if an existing inode holds an identical value. If such an
> inode is found, the ref count on that inode is incremented. On value
> removal the ref count is decremented and if it reaches zero the inode is
> deleted.
>
> The quota charging for such inodes is manually managed. Every reference
> holder is charged the full size as if there was no sharing happening.
> This is consistent with how xattr blocks are also charged.
>
> Signed-off-by: Tahsin Erdogan <tahsin@xxxxxxxxxx>
> ---
> v5:
>  - made ext4_meta_trans_blocks() static again since there are no
>    remaining users outside of inode.c
>  - initialize sbi->s_csum_seed when ea_inode feature is enabled
>  - use l_i_version to hold lower 32 bits of the xattr ref count.
>    This avoids clashes with old implementations which use i_mtime.
>    Since l_i_version is not available in HURD_COMPAT mode, fail mount
>    request when both ea_inode feature and HURD_COMPAT are set.
>  - when hash validation fails, fall back to old implementation
>    which has a backref to parent.
>  - fixed checkpatch.pl warning about using unsigned alone
>
> v4:
>  - eliminated xattr entry in the xattr inode to avoid complexity and
>    recursion in xattr update path. Now the ref count and hash are stored
>    in i_[c/m/a]time.tv_sec fields.
>  - some clean up in ext4_xattr_set_entry() to reduce code duplication and
>    complexity
>
> v3:
>  - use s_csum_seed for hash calculations when available
>  - return error on stored vs calculated hash mismatch
>
> v2:
>  - make dependency on crc32c dynamic
>  - update ext4_has_metadata_csum() and ext4_has_group_desc_csum() so that
>    they do not misinterpret existence of EXT4_SB(sb)->s_chksum_driver
>
>  fs/ext4/acl.c   |    5 +-
>  fs/ext4/ext4.h  |   23 +-
>  fs/ext4/inode.c |   13 +-
>  fs/ext4/super.c |   37 +-
>  fs/ext4/xattr.c | 1038 +++++++++++++++++++++++++++++++++++++++++--------------
>  fs/ext4/xattr.h |   17 +-
>  fs/mbcache.c    |    9 +-
>  7 files changed, 848 insertions(+), 294 deletions(-)
>
> diff --git a/fs/ext4/acl.c b/fs/ext4/acl.c
> index 74f7ac539e00..8db03e5c78bc 100644
> --- a/fs/ext4/acl.c
> +++ b/fs/ext4/acl.c
> @@ -238,7 +238,10 @@ ext4_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>         if (error)
>                 return error;
>  retry:
> -       credits = ext4_xattr_set_credits(inode, acl_size);
> +       error = ext4_xattr_set_credits(inode, acl_size, &credits);
> +       if (error)
> +               return error;
> +
>         handle = ext4_journal_start(inode, EXT4_HT_XATTR, credits);
>         if (IS_ERR(handle))
>                 return PTR_ERR(handle);
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index d79d8d7bee88..59e9488c4876 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1517,6 +1517,7 @@ struct ext4_sb_info {
>         long s_es_nr_inode;
>         struct ext4_es_stats s_es_stats;
>         struct mb_cache *s_mb_cache;
> +       struct mb_cache *s_ea_inode_cache;
>         spinlock_t s_es_lock ____cacheline_aligned_in_smp;
>
>         /* Ratelimit ext4 messages. */
> @@ -2099,7 +2100,11 @@ static inline struct ext4_inode *ext4_raw_inode(struct ext4_iloc *iloc)
>         return (struct ext4_inode *) (iloc->bh->b_data + iloc->offset);
>  }
>
> -#define ext4_is_quota_file(inode) IS_NOQUOTA(inode)
> +static inline bool ext4_is_quota_file(struct inode *inode)
> +{
> +       return IS_NOQUOTA(inode) &&
> +              !(EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL);
> +}
>
>  /*
>   * This structure is stuffed into the struct file's private_data field
> @@ -2482,7 +2487,6 @@ extern int ext4_truncate_restart_trans(handle_t *, struct inode *, int nblocks);
>  extern void ext4_set_inode_flags(struct inode *);
>  extern int ext4_alloc_da_blocks(struct inode *inode);
>  extern void ext4_set_aops(struct inode *inode);
> -extern int ext4_meta_trans_blocks(struct inode *, int nrblocks, int chunk);
>  extern int ext4_writepage_trans_blocks(struct inode *);
>  extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
>  extern int ext4_zero_partial_blocks(handle_t *handle, struct inode *inode,
> @@ -2709,19 +2713,20 @@ extern void ext4_group_desc_csum_set(struct super_block *sb, __u32 group,
>  extern int ext4_register_li_request(struct super_block *sb,
>                                     ext4_group_t first_not_zeroed);
>
> -static inline int ext4_has_group_desc_csum(struct super_block *sb)
> -{
> -       return ext4_has_feature_gdt_csum(sb) ||
> -              EXT4_SB(sb)->s_chksum_driver != NULL;
> -}
> -
>  static inline int ext4_has_metadata_csum(struct super_block *sb)
>  {
>         WARN_ON_ONCE(ext4_has_feature_metadata_csum(sb) &&
>                      !EXT4_SB(sb)->s_chksum_driver);
>
> -       return (EXT4_SB(sb)->s_chksum_driver != NULL);
> +       return ext4_has_feature_metadata_csum(sb) &&
> +              (EXT4_SB(sb)->s_chksum_driver != NULL);
>  }
> +
> +static inline int ext4_has_group_desc_csum(struct super_block *sb)
> +{
> +       return ext4_has_feature_gdt_csum(sb) || ext4_has_metadata_csum(sb);
> +}
> +
>  static inline ext4_fsblk_t ext4_blocks_count(struct ext4_super_block *es)
>  {
>         return ((ext4_fsblk_t)le32_to_cpu(es->s_blocks_count_hi) << 32) |
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index cd007f9757d1..ea95bd9eab81 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -139,6 +139,8 @@ static void ext4_invalidatepage(struct page *page, unsigned int offset,
>                                 unsigned int length);
>  static int __ext4_journalled_writepage(struct page *page, unsigned int len);
>  static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh);
> +static int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
> +                                 int pextents);
>
>  /*
>   * Test whether an inode is a fast symlink.
> @@ -4843,8 +4845,15 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
>         }
>         brelse(iloc.bh);
>         ext4_set_inode_flags(inode);
> -       if (ei->i_flags & EXT4_EA_INODE_FL)
> +
> +       if (ei->i_flags & EXT4_EA_INODE_FL) {
>                 ext4_xattr_inode_set_class(inode);
> +
> +               inode_lock(inode);
> +               inode->i_flags |= S_NOQUOTA;
> +               inode_unlock(inode);
> +       }
> +
>         unlock_new_inode(inode);
>         return inode;
>
> @@ -5503,7 +5512,7 @@ static int ext4_index_trans_blocks(struct inode *inode, int lblocks,
>   *
>   * Also account for superblock, inode, quota and xattr blocks
>   */
> -int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
> +static int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
>                                   int pextents)
>  {
>         ext4_group_t groups, ngroups = ext4_get_groups_count(inode->i_sb);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index b02a23ec92ca..2bfacd737bb6 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -927,6 +927,10 @@ static void ext4_put_super(struct super_block *sb)
>                 invalidate_bdev(sbi->journal_bdev);
>                 ext4_blkdev_remove(sbi);
>         }
> +       if (sbi->s_ea_inode_cache) {
> +               ext4_xattr_destroy_cache(sbi->s_ea_inode_cache);
> +               sbi->s_ea_inode_cache = NULL;
> +       }
>         if (sbi->s_mb_cache) {
>                 ext4_xattr_destroy_cache(sbi->s_mb_cache);
>                 sbi->s_mb_cache = NULL;
> @@ -1178,7 +1182,10 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
>         if (res)
>                 return res;
>  retry:
> -       credits = ext4_xattr_set_credits(inode, len);
> +       res = ext4_xattr_set_credits(inode, len, &credits);
> +       if (res)
> +               return res;
> +
>         handle = ext4_journal_start(inode, EXT4_HT_MISC, credits);
>         if (IS_ERR(handle))
>                 return PTR_ERR(handle);
> @@ -3445,7 +3452,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>         }
>
>         /* Load the checksum driver */
> -       if (ext4_has_feature_metadata_csum(sb)) {
> +       if (ext4_has_feature_metadata_csum(sb) ||
> +           ext4_has_feature_ea_inode(sb)) {
>                 sbi->s_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
>                 if (IS_ERR(sbi->s_chksum_driver)) {
>                         ext4_msg(sb, KERN_ERR, "Cannot load crc32c driver.");
> @@ -3467,7 +3475,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>         /* Precompute checksum seed for all metadata */
>         if (ext4_has_feature_csum_seed(sb))
>                 sbi->s_csum_seed = le32_to_cpu(es->s_checksum_seed);
> -       else if (ext4_has_metadata_csum(sb))
> +       else if (ext4_has_metadata_csum(sb) || ext4_has_feature_ea_inode(sb))
>                 sbi->s_csum_seed = ext4_chksum(sbi, ~0, es->s_uuid,
>                                                sizeof(es->s_uuid));
>
> @@ -3597,6 +3605,16 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>                                  "The Hurd can't support 64-bit file systems");
>                         goto failed_mount;
>                 }
> +
> +               /*
> +                * ea_inode feature uses l_i_version field which is not
> +                * available in HURD_COMPAT mode.
> +                */
> +               if (ext4_has_feature_ea_inode(sb)) {
> +                       ext4_msg(sb, KERN_ERR,
> +                                "ea_inode feature is not supported for Hurd");
> +                       goto failed_mount;
> +               }
>         }
>
>         if (IS_EXT2_SB(sb)) {
> @@ -4067,6 +4085,15 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>                 goto failed_mount_wq;
>         }
>
> +       if (ext4_has_feature_ea_inode(sb)) {
> +               sbi->s_ea_inode_cache = ext4_xattr_create_cache();
> +               if (!sbi->s_ea_inode_cache) {
> +                       ext4_msg(sb, KERN_ERR,
> +                                "Failed to create an s_ea_inode_cache");
> +                       goto failed_mount_wq;
> +               }
> +       }
> +
>         if ((DUMMY_ENCRYPTION_ENABLED(sbi) || ext4_has_feature_encrypt(sb)) &&
>             (blocksize != PAGE_SIZE)) {
>                 ext4_msg(sb, KERN_ERR,
> @@ -4296,6 +4323,10 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>         if (EXT4_SB(sb)->rsv_conversion_wq)
>                 destroy_workqueue(EXT4_SB(sb)->rsv_conversion_wq);
>  failed_mount_wq:
> +       if (sbi->s_ea_inode_cache) {
> +               ext4_xattr_destroy_cache(sbi->s_ea_inode_cache);
> +               sbi->s_ea_inode_cache = NULL;
> +       }
>         if (sbi->s_mb_cache) {
>                 ext4_xattr_destroy_cache(sbi->s_mb_cache);
>                 sbi->s_mb_cache = NULL;
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 0484df8dadd1..d7e60358ec91 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -108,6 +108,9 @@ const struct xattr_handler *ext4_xattr_handlers[] = {
>  #define EXT4_GET_MB_CACHE(inode)       (((struct ext4_sb_info *) \
>                                 inode->i_sb->s_fs_info)->s_mb_cache)
>
> +#define EA_INODE_CACHE(inode)  (((struct ext4_sb_info *) \
> +                               inode->i_sb->s_fs_info)->s_ea_inode_cache)
> +
>  static int
>  ext4_expand_inode_array(struct ext4_xattr_inode_array **ea_inode_array,
>                         struct inode *inode);
> @@ -280,15 +283,44 @@ ext4_xattr_find_entry(struct ext4_xattr_entry **pentry, int name_index,
>         return cmp ? -ENODATA : 0;
>  }
>
> +static u32
> +ext4_xattr_inode_hash(struct ext4_sb_info *sbi, const void *buffer, size_t size)
> +{
> +       return ext4_chksum(sbi, sbi->s_csum_seed, buffer, size);
> +}
> +
> +static u64 ext4_xattr_inode_get_ref(struct inode *ea_inode)
> +{
> +       return ((u64)ea_inode->i_ctime.tv_sec << 32) |
> +              ((u32)ea_inode->i_version);
> +}
> +
> +static void ext4_xattr_inode_set_ref(struct inode *ea_inode, u64 ref_count)
> +{
> +       ea_inode->i_ctime.tv_sec = (u32)(ref_count >> 32);
> +       ea_inode->i_version = (u32)ref_count;
> +}
> +
> +static u32 ext4_xattr_inode_get_hash(struct inode *ea_inode)
> +{
> +       return (u32)ea_inode->i_atime.tv_sec;
> +}
> +
> +static void ext4_xattr_inode_set_hash(struct inode *ea_inode, u32 hash)
> +{
> +       ea_inode->i_atime.tv_sec = hash;
> +}
> +
>  /*
>   * Read the EA value from an inode.
>   */
>  static int ext4_xattr_inode_read(struct inode *ea_inode, void *buf, size_t size)
>  {
>         unsigned long block = 0;
> -       struct buffer_head *bh = NULL;
> +       struct buffer_head *bh;
>         int blocksize = ea_inode->i_sb->s_blocksize;
>         size_t csize, copied = 0;
> +       void *copy_pos = buf;
>
>         while (copied < size) {
>                 csize = (size - copied) > blocksize ? blocksize : size - copied;
> @@ -298,10 +330,10 @@ static int ext4_xattr_inode_read(struct inode *ea_inode, void *buf, size_t size)
>                 if (!bh)
>                         return -EFSCORRUPTED;
>
> -               memcpy(buf, bh->b_data, csize);
> +               memcpy(copy_pos, bh->b_data, csize);
>                 brelse(bh);
>
> -               buf += csize;
> +               copy_pos += csize;
>                 block += 1;
>                 copied += csize;
>         }
> @@ -317,29 +349,24 @@ static int ext4_xattr_inode_iget(struct inode *parent, unsigned long ea_ino,
>         inode = ext4_iget(parent->i_sb, ea_ino);
>         if (IS_ERR(inode)) {
>                 err = PTR_ERR(inode);
> -               ext4_error(parent->i_sb, "error while reading EA inode %lu "
> -                          "err=%d", ea_ino, err);
> +               ext4_error(parent->i_sb,
> +                          "error while reading EA inode %lu err=%d", ea_ino,
> +                          err);
>                 return err;
>         }
>
>         if (is_bad_inode(inode)) {
> -               ext4_error(parent->i_sb, "error while reading EA inode %lu "
> -                          "is_bad_inode", ea_ino);
> +               ext4_error(parent->i_sb,
> +                          "error while reading EA inode %lu is_bad_inode",
> +                          ea_ino);
>                 err = -EIO;
>                 goto error;
>         }
>
> -       if (EXT4_XATTR_INODE_GET_PARENT(inode) != parent->i_ino ||
> -           inode->i_generation != parent->i_generation) {
> -               ext4_error(parent->i_sb, "Backpointer from EA inode %lu "
> -                          "to parent is invalid.", ea_ino);
> -               err = -EINVAL;
> -               goto error;
> -       }
> -
>         if (!(EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL)) {
> -               ext4_error(parent->i_sb, "EA inode %lu does not have "
> -                          "EXT4_EA_INODE_FL flag set.\n", ea_ino);
> +               ext4_error(parent->i_sb,
> +                          "EA inode %lu does not have EXT4_EA_INODE_FL flag",
> +                           ea_ino);
>                 err = -EINVAL;
>                 goto error;
>         }
> @@ -351,6 +378,20 @@ static int ext4_xattr_inode_iget(struct inode *parent, unsigned long ea_ino,
>         return err;
>  }
>
> +static int
> +ext4_xattr_inode_verify_hash(struct inode *ea_inode, void *buffer, size_t size)
> +{
> +       u32 hash;
> +
> +       /* Verify stored hash matches calculated hash. */
> +       hash = ext4_xattr_inode_hash(EXT4_SB(ea_inode->i_sb), buffer, size);
> +       if (hash != ext4_xattr_inode_get_hash(ea_inode))
> +               return -EFSCORRUPTED;
> +       return 0;
> +}
> +
> +#define EXT4_XATTR_INODE_GET_PARENT(inode) ((__u32)(inode)->i_mtime.tv_sec)
> +
>  /*
>   * Read the value from the EA inode.
>   */
> @@ -358,17 +399,53 @@ static int
>  ext4_xattr_inode_get(struct inode *inode, unsigned long ea_ino, void *buffer,
>                      size_t size)
>  {
> +       struct mb_cache *ea_inode_cache = EA_INODE_CACHE(inode);
>         struct inode *ea_inode;
> -       int ret;
> +       int err;
>
> -       ret = ext4_xattr_inode_iget(inode, ea_ino, &ea_inode);
> -       if (ret)
> -               return ret;
> +       err = ext4_xattr_inode_iget(inode, ea_ino, &ea_inode);
> +       if (err) {
> +               ea_inode = NULL;
> +               goto out;
> +       }
>
> -       ret = ext4_xattr_inode_read(ea_inode, buffer, size);
> -       iput(ea_inode);
> +       if (i_size_read(ea_inode) != size) {
> +               ext4_warning_inode(ea_inode,
> +                                  "ea_inode file size=%llu entry size=%zu",
> +                                  i_size_read(ea_inode), size);
> +               err = -EFSCORRUPTED;
> +               goto out;
> +       }
>
> -       return ret;
> +       err = ext4_xattr_inode_read(ea_inode, buffer, size);
> +       if (err)
> +               goto out;
> +
> +       err = ext4_xattr_inode_verify_hash(ea_inode, buffer, size);
> +       /*
> +        * Compatibility check for old Lustre ea_inode implementation. Old
> +        * version does not have hash validation, but it has a backpointer
> +        * from ea_inode to the parent inode.
> +        */
> +       if (err == -EFSCORRUPTED) {
> +               if (EXT4_XATTR_INODE_GET_PARENT(ea_inode) != inode->i_ino ||
> +                   ea_inode->i_generation != inode->i_generation) {
> +                       ext4_warning_inode(ea_inode,
> +                                          "EA inode hash validation failed");
> +                       goto out;
> +               }
> +               /* Do not add ea_inode to the cache. */
> +               ea_inode_cache = NULL;
> +       } else if (err)
> +               goto out;
> +
> +       if (ea_inode_cache)
> +               mb_cache_entry_create(ea_inode_cache, GFP_NOFS,
> +                                     ext4_xattr_inode_get_hash(ea_inode),
> +                                     ea_inode->i_ino, true /* reusable */);
> +out:
> +       iput(ea_inode);
> +       return err;
>  }
>
>  static int
> @@ -657,6 +734,101 @@ static void ext4_xattr_update_super_block(handle_t *handle,
>         }
>  }
>
> +static inline size_t round_up_cluster(struct inode *inode, size_t length)
> +{
> +       struct super_block *sb = inode->i_sb;
> +       size_t cluster_size = 1 << (EXT4_SB(sb)->s_cluster_bits +
> +                                   inode->i_blkbits);
> +       size_t mask = ~(cluster_size - 1);
> +
> +       return (length + cluster_size - 1) & mask;
> +}
> +
> +static int ext4_xattr_inode_alloc_quota(struct inode *inode, size_t len)
> +{
> +       int err;
> +
> +       err = dquot_alloc_inode(inode);
> +       if (err)
> +               return err;
> +       err = dquot_alloc_space_nodirty(inode, round_up_cluster(inode, len));
> +       if (err)
> +               dquot_free_inode(inode);
> +       return err;
> +}
> +
> +static void ext4_xattr_inode_free_quota(struct inode *inode, size_t len)
> +{
> +       dquot_free_space_nodirty(inode, round_up_cluster(inode, len));
> +       dquot_free_inode(inode);
> +}
> +
> +static int __ext4_xattr_set_credits(struct super_block *sb,
> +                                   struct buffer_head *block_bh,
> +                                   size_t value_len)
> +{
> +       int credits;
> +       int blocks;
> +
> +       /*
> +        * 1) Owner inode update
> +        * 2) Ref count update on old xattr block
> +        * 3) new xattr block
> +        * 4) block bitmap update for new xattr block
> +        * 5) group descriptor for new xattr block
> +        */
> +       credits = 5;
> +
> +       /* We are done if ea_inode feature is not enabled. */
> +       if (!ext4_has_feature_ea_inode(sb))
> +               return credits;
> +
> +       /* New ea_inode, inode map, block bitmap, group descriptor. */
> +       credits += 4;
> +
> +       /* Data blocks. */
> +       blocks = (value_len + sb->s_blocksize - 1) >> sb->s_blocksize_bits;
> +
> +       /* Indirection block or one level of extent tree. */
> +       blocks += 1;
> +
> +       /* Block bitmap and group descriptor updates for each block. */
> +       credits += blocks * 2;
> +
> +       /* Blocks themselves. */
> +       credits += blocks;
> +
> +       /* Dereference ea_inode holding old xattr value.
> +        * Old ea_inode, inode map, block bitmap, group descriptor.
> +        */
> +       credits += 4;
> +
> +       /* Data blocks for old ea_inode. */
> +       blocks = XATTR_SIZE_MAX >> sb->s_blocksize_bits;
> +
> +       /* Indirection block or one level of extent tree for old ea_inode. */
> +       blocks += 1;
> +
> +       /* Block bitmap and group descriptor updates for each block. */
> +       credits += blocks * 2;
> +
> +       /* Quota updates. */
> +       credits += EXT4_MAXQUOTAS_TRANS_BLOCKS(sb);
> +
> +       /* We may need to clone the existing xattr block in which case we need
> +        * to increment ref counts for existing ea_inodes referenced by it.
> +        */
> +       if (block_bh) {
> +               struct ext4_xattr_entry *entry = BFIRST(block_bh);
> +
> +               for (; !IS_LAST_ENTRY(entry); entry = EXT4_XATTR_NEXT(entry))
> +                       if (entry->e_value_inum)
> +                               /* Ref count update on ea_inode. */
> +                               credits += 1;
> +       }
> +       return credits;
> +}
> +
>  static int ext4_xattr_ensure_credits(handle_t *handle, struct inode *inode,
>                                      int credits, struct buffer_head *bh,
>                                      bool dirty, bool block_csum)
> @@ -706,12 +878,140 @@ static int ext4_xattr_ensure_credits(handle_t *handle, struct inode *inode,
>         return 0;
>  }
>
> +static int ext4_xattr_inode_update_ref(handle_t *handle, struct inode *ea_inode,
> +                                      int ref_change)
> +{
> +       struct mb_cache *ea_inode_cache = EA_INODE_CACHE(ea_inode);
> +       struct ext4_iloc iloc;
> +       s64 ref_count;
> +       u32 hash;
> +       int ret;
> +
> +       inode_lock(ea_inode);
> +
> +       ret = ext4_reserve_inode_write(handle, ea_inode, &iloc);
> +       if (ret) {
> +               iloc.bh = NULL;
> +               goto out;
> +       }
> +
> +       ref_count = ext4_xattr_inode_get_ref(ea_inode);
> +       ref_count += ref_change;
> +       ext4_xattr_inode_set_ref(ea_inode, ref_count);
> +
> +       if (ref_change > 0) {
> +               WARN_ONCE(ref_count <= 0, "EA inode %lu ref_count=%lld",
> +                         ea_inode->i_ino, ref_count);
> +
> +               if (ref_count == 1) {
> +                       WARN_ONCE(ea_inode->i_nlink, "EA inode %lu i_nlink=%u",
> +                                 ea_inode->i_ino, ea_inode->i_nlink);
> +
> +                       set_nlink(ea_inode, 1);
> +                       ext4_orphan_del(handle, ea_inode);
> +
> +                       hash = ext4_xattr_inode_get_hash(ea_inode);
> +                       mb_cache_entry_create(ea_inode_cache, GFP_NOFS, hash,
> +                                             ea_inode->i_ino,
> +                                             true /* reusable */);
> +               }
> +       } else {
> +               WARN_ONCE(ref_count < 0, "EA inode %lu ref_count=%lld",
> +                         ea_inode->i_ino, ref_count);
> +
> +               if (ref_count == 0) {
> +                       WARN_ONCE(ea_inode->i_nlink != 1,
> +                                 "EA inode %lu i_nlink=%u",
> +                                 ea_inode->i_ino, ea_inode->i_nlink);
> +
> +                       clear_nlink(ea_inode);
> +                       ext4_orphan_add(handle, ea_inode);
> +
> +                       hash = ext4_xattr_inode_get_hash(ea_inode);
> +                       mb_cache_entry_delete(ea_inode_cache, hash,
> +                                             ea_inode->i_ino);
> +               }
> +       }
> +
> +       ret = ext4_mark_iloc_dirty(handle, ea_inode, &iloc);
> +       iloc.bh = NULL;
> +       if (ret)
> +               ext4_warning_inode(ea_inode,
> +                                  "ext4_mark_iloc_dirty() failed ret=%d", ret);
> +out:
> +       brelse(iloc.bh);
> +       inode_unlock(ea_inode);
> +       return ret;
> +}
> +
> +static int ext4_xattr_inode_inc_ref(handle_t *handle, struct inode *ea_inode)
> +{
> +       return ext4_xattr_inode_update_ref(handle, ea_inode, 1);
> +}
> +
> +static int ext4_xattr_inode_dec_ref(handle_t *handle, struct inode *ea_inode)
> +{
> +       return ext4_xattr_inode_update_ref(handle, ea_inode, -1);
> +}
> +
> +static int ext4_xattr_inode_inc_ref_all(handle_t *handle, struct inode *parent,
> +                                       struct ext4_xattr_entry *first)
> +{
> +       struct inode *ea_inode;
> +       struct ext4_xattr_entry *entry;
> +       struct ext4_xattr_entry *failed_entry;
> +       unsigned int ea_ino;
> +       int err, saved_err;
> +
> +       for (entry = first; !IS_LAST_ENTRY(entry);
> +            entry = EXT4_XATTR_NEXT(entry)) {
> +               if (!entry->e_value_inum)
> +                       continue;
> +               ea_ino = le32_to_cpu(entry->e_value_inum);
> +               err = ext4_xattr_inode_iget(parent, ea_ino, &ea_inode);
> +               if (err)
> +                       goto cleanup;
> +               err = ext4_xattr_inode_inc_ref(handle, ea_inode);
> +               if (err) {
> +                       ext4_warning_inode(ea_inode, "inc ref error %d", err);
> +                       iput(ea_inode);
> +                       goto cleanup;
> +               }
> +               iput(ea_inode);
> +       }
> +       return 0;
> +
> +cleanup:
> +       saved_err = err;
> +       failed_entry = entry;
> +
> +       for (entry = first; entry != failed_entry;
> +            entry = EXT4_XATTR_NEXT(entry)) {
> +               if (!entry->e_value_inum)
> +                       continue;
> +               ea_ino = le32_to_cpu(entry->e_value_inum);
> +               err = ext4_xattr_inode_iget(parent, ea_ino, &ea_inode);
> +               if (err) {
> +                       ext4_warning(parent->i_sb,
> +                                    "cleanup ea_ino %u iget error %d", ea_ino,
> +                                    err);
> +                       continue;
> +               }
> +               err = ext4_xattr_inode_dec_ref(handle, ea_inode);
> +               if (err)
> +                       ext4_warning_inode(ea_inode, "cleanup dec ref error %d",
> +                                          err);
> +               iput(ea_inode);
> +       }
> +       return saved_err;
> +}
> +
>  static void
> -ext4_xattr_inode_remove_all(handle_t *handle, struct inode *parent,
> -                           struct buffer_head *bh,
> -                           struct ext4_xattr_entry *first, bool block_csum,
> -                           struct ext4_xattr_inode_array **ea_inode_array,
> -                           int extra_credits)
> +ext4_xattr_inode_dec_ref_all(handle_t *handle, struct inode *parent,
> +                            struct buffer_head *bh,
> +                            struct ext4_xattr_entry *first, bool block_csum,
> +                            struct ext4_xattr_inode_array **ea_inode_array,
> +                            int extra_credits, bool skip_quota)
>  {
>         struct inode *ea_inode;
>         struct ext4_xattr_entry *entry;
> @@ -748,10 +1048,16 @@ ext4_xattr_inode_remove_all(handle_t *handle, struct inode *parent,
>                         continue;
>                 }
>
> -               inode_lock(ea_inode);
> -               clear_nlink(ea_inode);
> -               ext4_orphan_add(handle, ea_inode);
> -               inode_unlock(ea_inode);
> +               err = ext4_xattr_inode_dec_ref(handle, ea_inode);
> +               if (err) {
> +                       ext4_warning_inode(ea_inode, "ea_inode dec ref err=%d",
> +                                          err);
> +                       continue;
> +               }
> +
> +               if (!skip_quota)
> +                       ext4_xattr_inode_free_quota(parent,
> +                                             le32_to_cpu(entry->e_value_size));
>
>                 /*
>                  * Forget about ea_inode within the same transaction that
> @@ -785,7 +1091,9 @@ ext4_xattr_inode_remove_all(handle_t *handle, struct inode *parent,
>   */
>  static void
>  ext4_xattr_release_block(handle_t *handle, struct inode *inode,
> -                        struct buffer_head *bh)
> +                        struct buffer_head *bh,
> +                        struct ext4_xattr_inode_array **ea_inode_array,
> +                        int extra_credits)
>  {
>         struct mb_cache *ext4_mb_cache = EXT4_GET_MB_CACHE(inode);
>         u32 hash, ref;
> @@ -808,6 +1116,14 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
>                 mb_cache_entry_delete(ext4_mb_cache, hash, bh->b_blocknr);
>                 get_bh(bh);
>                 unlock_buffer(bh);
> +
> +               if (ext4_has_feature_ea_inode(inode->i_sb))
> +                       ext4_xattr_inode_dec_ref_all(handle, inode, bh,
> +                                                    BFIRST(bh),
> +                                                    true /* block_csum */,
> +                                                    ea_inode_array,
> +                                                    extra_credits,
> +                                                    true /* skip_quota */);
>                 ext4_free_blocks(handle, inode, bh, 0, 1,
>                                  EXT4_FREE_BLOCKS_METADATA |
>                                  EXT4_FREE_BLOCKS_FORGET);
> @@ -879,8 +1195,8 @@ static int ext4_xattr_inode_write(handle_t *handle, struct inode *ea_inode,
>  {
>         struct buffer_head *bh = NULL;
>         unsigned long block = 0;
> -       unsigned blocksize = ea_inode->i_sb->s_blocksize;
> -       unsigned max_blocks = (bufsize + blocksize - 1) >> ea_inode->i_blkbits;
> +       int blocksize = ea_inode->i_sb->s_blocksize;
> +       int max_blocks = (bufsize + blocksize - 1) >> ea_inode->i_blkbits;
>         int csize, wsize = 0;
>         int ret = 0;
>         int retries = 0;
> @@ -948,7 +1264,7 @@ static int ext4_xattr_inode_write(handle_t *handle, struct inode *ea_inode,
>   * Create an inode to store the value of a large EA.
>   */
>  static struct inode *ext4_xattr_inode_create(handle_t *handle,
> -                                            struct inode *inode)
> +                                            struct inode *inode, u32 hash)
>  {
>         struct inode *ea_inode = NULL;
>         uid_t owner[2] = { i_uid_read(inode), i_gid_read(inode) };
> @@ -966,67 +1282,115 @@ static struct inode *ext4_xattr_inode_create(handle_t *handle,
>                 ea_inode->i_fop = &ext4_file_operations;
>                 ext4_set_aops(ea_inode);
>                 ext4_xattr_inode_set_class(ea_inode);
> -               ea_inode->i_generation = inode->i_generation;
> -               EXT4_I(ea_inode)->i_flags |= EXT4_EA_INODE_FL;
> -
> -               /*
> -                * A back-pointer from EA inode to parent inode will be useful
> -                * for e2fsck.
> -                */
> -               EXT4_XATTR_INODE_SET_PARENT(ea_inode, inode->i_ino);
>                 unlock_new_inode(ea_inode);
> -               err = ext4_inode_attach_jinode(ea_inode);
> +               ext4_xattr_inode_set_ref(ea_inode, 1);
> +               ext4_xattr_inode_set_hash(ea_inode, hash);
> +               err = ext4_mark_inode_dirty(handle, ea_inode);
> +               if (!err)
> +                       err = ext4_inode_attach_jinode(ea_inode);
>                 if (err) {
>                         iput(ea_inode);
>                         return ERR_PTR(err);
>                 }
> +
> +               /*
> +                * Xattr inodes are shared therefore quota charging is performed
> +                * at a higher level.
> +                */
> +               dquot_free_inode(ea_inode);
> +               dquot_drop(ea_inode);
> +               inode_lock(ea_inode);
> +               ea_inode->i_flags |= S_NOQUOTA;
> +               inode_unlock(ea_inode);
>         }
>
>         return ea_inode;
>  }
>
> -/*
> - * Unlink the inode storing the value of the EA.
> - */
> -int ext4_xattr_inode_unlink(struct inode *inode, unsigned long ea_ino)
> +static struct inode *
> +ext4_xattr_inode_cache_find(struct inode *inode, const void *value,
> +                           size_t value_len, u32 hash)
>  {
> -       struct inode *ea_inode = NULL;
> -       int err;
> +       struct inode *ea_inode;
> +       struct mb_cache_entry *ce;
> +       struct mb_cache *ea_inode_cache = EA_INODE_CACHE(inode);
> +       void *ea_data;
>
> -       err = ext4_xattr_inode_iget(inode, ea_ino, &ea_inode);
> -       if (err)
> -               return err;
> +       ce = mb_cache_entry_find_first(ea_inode_cache, hash);
> +       if (!ce)
> +               return NULL;
>
> -       clear_nlink(ea_inode);
> -       iput(ea_inode);
> +       ea_data = ext4_kvmalloc(value_len, GFP_NOFS);
> +       if (!ea_data) {
> +               mb_cache_entry_put(ea_inode_cache, ce);
> +               return NULL;
> +       }
>
> -       return 0;
> +       while (ce) {
> +               ea_inode = ext4_iget(inode->i_sb, ce->e_value);
> +               if (!IS_ERR(ea_inode) &&
> +                   !is_bad_inode(ea_inode) &&
> +                   (EXT4_I(ea_inode)->i_flags & EXT4_EA_INODE_FL) &&
> +                   i_size_read(ea_inode) == value_len &&
> +                   !ext4_xattr_inode_read(ea_inode, ea_data, value_len) &&
> +                   !ext4_xattr_inode_verify_hash(ea_inode, ea_data,
> +                                                 value_len) &&
> +                   !memcmp(value, ea_data, value_len)) {
> +                       mb_cache_entry_touch(ea_inode_cache, ce);
> +                       mb_cache_entry_put(ea_inode_cache, ce);
> +                       kvfree(ea_data);
> +                       return ea_inode;
> +               }
> +
> +               if (!IS_ERR(ea_inode))
> +                       iput(ea_inode);
> +               ce = mb_cache_entry_find_next(ea_inode_cache, ce);
> +       }
> +       kvfree(ea_data);
> +       return NULL;
>  }
>
>  /*
>   * Add value of the EA in an inode.
>   */
> -static int ext4_xattr_inode_set(handle_t *handle, struct inode *inode,
> -                               unsigned long *ea_ino, const void *value,
> -                               size_t value_len)
> +static int ext4_xattr_inode_lookup_create(handle_t *handle, struct inode *inode,
> +                                         const void *value, size_t value_len,
> +                                         struct inode **ret_inode)
>  {
>         struct inode *ea_inode;
> +       u32 hash;
>         int err;
>
> +       hash = ext4_xattr_inode_hash(EXT4_SB(inode->i_sb), value, value_len);
> +       ea_inode = ext4_xattr_inode_cache_find(inode, value, value_len, hash);
> +       if (ea_inode) {
> +               err = ext4_xattr_inode_inc_ref(handle, ea_inode);
> +               if (err) {
> +                       iput(ea_inode);
> +                       return err;
> +               }
> +
> +               *ret_inode = ea_inode;
> +               return 0;
> +       }
> +
>         /* Create an inode for the EA value */
> -       ea_inode = ext4_xattr_inode_create(handle, inode);
> +       ea_inode = ext4_xattr_inode_create(handle, inode, hash);
>         if (IS_ERR(ea_inode))
>                 return PTR_ERR(ea_inode);
>
>         err = ext4_xattr_inode_write(handle, ea_inode, value, value_len);
> -       if (err)
> -               clear_nlink(ea_inode);
> -       else
> -               *ea_ino = ea_inode->i_ino;
> +       if (err) {
> +               ext4_xattr_inode_dec_ref(handle, ea_inode);
> +               iput(ea_inode);
> +               return err;
> +       }
>
> -       iput(ea_inode);
> +       mb_cache_entry_create(EA_INODE_CACHE(inode), GFP_NOFS, hash,
> +                             ea_inode->i_ino, true /* reusable */);
>
> -       return err;
> +       *ret_inode = ea_inode;
> +       return 0;
>  }
>
>  static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
> @@ -1034,9 +1398,37 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
>                                 handle_t *handle, struct inode *inode)
>  {
>         struct ext4_xattr_entry *last;
> -       size_t free, min_offs = s->end - s->base, name_len = strlen(i->name);
> +       struct ext4_xattr_entry *here = s->here;
> +       size_t min_offs = s->end - s->base, name_len = strlen(i->name);
>         int in_inode = i->in_inode;
> -       int rc;
> +       struct inode *old_ea_inode = NULL;
> +       struct inode *new_ea_inode = NULL;
> +       size_t old_size, new_size;
> +       int ret;
> +
> +       /* Space used by old and new values. */
> +       old_size = (!s->not_found && !here->e_value_inum) ?
> +                       EXT4_XATTR_SIZE(le32_to_cpu(here->e_value_size)) : 0;
> +       new_size = (i->value && !in_inode) ? EXT4_XATTR_SIZE(i->value_len) : 0;
> +
> +       /*
> +        * Optimization for the simple case when old and new values have the
> +        * same padded sizes. Not applicable if external inodes are involved.
> +        */
> +       if (new_size && new_size == old_size) {
> +               size_t offs = le16_to_cpu(here->e_value_offs);
> +               void *val = s->base + offs;
> +
> +               here->e_value_size = cpu_to_le32(i->value_len);
> +               if (i->value == EXT4_ZERO_XATTR_VALUE) {
> +                       memset(val, 0, new_size);
> +               } else {
> +                       memcpy(val, i->value, i->value_len);
> +                       /* Clear padding bytes. */
> +                       memset(val + i->value_len, 0, new_size - i->value_len);
> +               }
> +               return 0;
> +       }
>
>         /* Compute min_offs and last. */
>         last = s->first;
> @@ -1047,122 +1439,148 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
>                                 min_offs = offs;
>                 }
>         }
> -       free = min_offs - ((void *)last - s->base) - sizeof(__u32);
> -       if (!s->not_found) {
> -               if (!in_inode &&
> -                   !s->here->e_value_inum && s->here->e_value_size) {
> -                       size_t size = le32_to_cpu(s->here->e_value_size);
> -                       free += EXT4_XATTR_SIZE(size);
> -               }
> -               free += EXT4_XATTR_LEN(name_len);
> -       }
> +
> +       /* Check whether we have enough space. */
>         if (i->value) {
> -               size_t value_len = EXT4_XATTR_SIZE(i->value_len);
> +               size_t free;
>
> -               if (in_inode)
> -                       value_len = 0;
> +               free = min_offs - ((void *)last - s->base) - sizeof(__u32);
> +               if (!s->not_found)
> +                       free += EXT4_XATTR_LEN(name_len) + old_size;
>
> -               if (free < EXT4_XATTR_LEN(name_len) + value_len)
> -                       return -ENOSPC;
> +               if (free < EXT4_XATTR_LEN(name_len) + new_size) {
> +                       ret = -ENOSPC;
> +                       goto out;
> +               }
>         }
>
> -       if (i->value && s->not_found) {
> -               /* Insert the new name. */
> -               size_t size = EXT4_XATTR_LEN(name_len);
> -               size_t rest = (void *)last - (void *)s->here + sizeof(__u32);
> -               memmove((void *)s->here + size, s->here, rest);
> -               memset(s->here, 0, size);
> -               s->here->e_name_index = i->name_index;
> -               s->here->e_name_len = name_len;
> -               memcpy(s->here->e_name, i->name, name_len);
> -       } else {
> -               if (!s->here->e_value_inum && s->here->e_value_size &&
> -                   s->here->e_value_offs > 0) {
> -                       void *first_val = s->base + min_offs;
> -                       size_t offs = le16_to_cpu(s->here->e_value_offs);
> -                       void *val = s->base + offs;
> -                       size_t size = EXT4_XATTR_SIZE(
> -                               le32_to_cpu(s->here->e_value_size));
> -
> -                       if (i->value && size == EXT4_XATTR_SIZE(i->value_len)) {
> -                               /* The old and the new value have the same
> -                                  size. Just replace. */
> -                               s->here->e_value_size =
> -                                       cpu_to_le32(i->value_len);
> -                               if (i->value == EXT4_ZERO_XATTR_VALUE) {
> -                                       memset(val, 0, size);
> -                               } else {
> -                                       /* Clear pad bytes first. */
> -                                       memset(val + size - EXT4_XATTR_PAD, 0,
> -                                              EXT4_XATTR_PAD);
> -                                       memcpy(val, i->value, i->value_len);
> -                               }
> -                               return 0;
> -                       }
> +       /*
> +        * Getting access to old and new ea inodes is subject to failures.
> +        * Finish that work before doing any modifications to the xattr data.
> +        */
> +       if (!s->not_found && here->e_value_inum) {
> +               ret = ext4_xattr_inode_iget(inode,
> +                                           le32_to_cpu(here->e_value_inum),
> +                                           &old_ea_inode);
> +               if (ret) {
> +                       old_ea_inode = NULL;
> +                       goto out;
> +               }
> +       }
> +       if (i->value && in_inode) {
> +               WARN_ON_ONCE(!i->value_len);
>
> -                       /* Remove the old value. */
> -                       memmove(first_val + size, first_val, val - first_val);
> -                       memset(first_val, 0, size);
> -                       s->here->e_value_size = 0;
> -                       s->here->e_value_offs = 0;
> -                       min_offs += size;
> -
> -                       /* Adjust all value offsets. */
> -                       last = s->first;
> -                       while (!IS_LAST_ENTRY(last)) {
> -                               size_t o = le16_to_cpu(last->e_value_offs);
> -                               if (!last->e_value_inum &&
> -                                   last->e_value_size && o < offs)
> -                                       last->e_value_offs =
> -                                               cpu_to_le16(o + size);
> -                               last = EXT4_XATTR_NEXT(last);
> -                       }
> +               ret = ext4_xattr_inode_alloc_quota(inode, i->value_len);
> +               if (ret)
> +                       goto out;
> +
> +               ret = ext4_xattr_inode_lookup_create(handle, inode, i->value,
> +                                                    i->value_len,
> +                                                    &new_ea_inode);
> +               if (ret) {
> +                       new_ea_inode = NULL;
> +                       ext4_xattr_inode_free_quota(inode, i->value_len);
> +                       goto out;
>                 }
> -               if (s->here->e_value_inum) {
> -                       ext4_xattr_inode_unlink(inode,
> -                                           le32_to_cpu(s->here->e_value_inum));
> -                       s->here->e_value_inum = 0;
> +       }
> +
> +       if (old_ea_inode) {
> +               /* We are ready to release ref count on the old_ea_inode. */
> +               ret = ext4_xattr_inode_dec_ref(handle, old_ea_inode);
> +               if (ret) {
> +                       /* Release newly required ref count on new_ea_inode. */
> +                       if (new_ea_inode) {
> +                               int err;
> +
> +                               err = ext4_xattr_inode_dec_ref(handle,
> +                                                              new_ea_inode);
> +                               if (err)
> +                                       ext4_warning_inode(new_ea_inode,
> +                                                 "dec ref new_ea_inode err=%d",
> +                                                 err);
> +                               ext4_xattr_inode_free_quota(inode,
> +                                                           i->value_len);
> +                       }
> +                       goto out;
>                 }
> -               if (!i->value) {
> -                       /* Remove the old name. */
> -                       size_t size = EXT4_XATTR_LEN(name_len);
> -                       last = ENTRY((void *)last - size);
> -                       memmove(s->here, (void *)s->here + size,
> -                               (void *)last - (void *)s->here + sizeof(__u32));
> -                       memset(last, 0, size);
> +
> +               ext4_xattr_inode_free_quota(inode,
> +                                           le32_to_cpu(here->e_value_size));
> +       }
> +
> +       /* No failures allowed past this point. */
> +
> +       if (!s->not_found && here->e_value_offs) {
> +               /* Remove the old value. */
> +               void *first_val = s->base + min_offs;
> +               size_t offs = le16_to_cpu(here->e_value_offs);
> +               void *val = s->base + offs;
> +
> +               memmove(first_val + old_size, first_val, val - first_val);
> +               memset(first_val, 0, old_size);
> +               min_offs += old_size;
> +
> +               /* Adjust all value offsets. */
> +               last = s->first;
> +               while (!IS_LAST_ENTRY(last)) {
> +                       size_t o = le16_to_cpu(last->e_value_offs);
> +
> +                       if (!last->e_value_inum &&
> +                           last->e_value_size && o < offs)
> +                               last->e_value_offs = cpu_to_le16(o + old_size);
> +                       last = EXT4_XATTR_NEXT(last);
>                 }
>         }
>
> +       if (!i->value) {
> +               /* Remove old name. */
> +               size_t size = EXT4_XATTR_LEN(name_len);
> +
> +               last = ENTRY((void *)last - size);
> +               memmove(here, (void *)here + size,
> +                       (void *)last - (void *)here + sizeof(__u32));
> +               memset(last, 0, size);
> +       } else if (s->not_found) {
> +               /* Insert new name. */
> +               size_t size = EXT4_XATTR_LEN(name_len);
> +               size_t rest = (void *)last - (void *)here + sizeof(__u32);
> +
> +               memmove((void *)here + size, here, rest);
> +               memset(here, 0, size);
> +               here->e_name_index = i->name_index;
> +               here->e_name_len = name_len;
> +               memcpy(here->e_name, i->name, name_len);
> +       } else {
> +               /* This is an update, reset value info. */
> +               here->e_value_inum = 0;
> +               here->e_value_offs = 0;
> +               here->e_value_size = 0;
> +       }
> +
>         if (i->value) {
> -               /* Insert the new value. */
> +               /* Insert new value. */
>                 if (in_inode) {
> -                       unsigned long ea_ino =
> -                               le32_to_cpu(s->here->e_value_inum);
> -                       rc = ext4_xattr_inode_set(handle, inode, &ea_ino,
> -                                                 i->value, i->value_len);
> -                       if (rc)
> -                               goto out;
> -                       s->here->e_value_inum = cpu_to_le32(ea_ino);
> -                       s->here->e_value_offs = 0;
> +                       here->e_value_inum = cpu_to_le32(new_ea_inode->i_ino);
>                 } else if (i->value_len) {
> -                       size_t size = EXT4_XATTR_SIZE(i->value_len);
> -                       void *val = s->base + min_offs - size;
> -                       s->here->e_value_offs = cpu_to_le16(min_offs - size);
> -                       s->here->e_value_inum = 0;
> +                       void *val = s->base + min_offs - new_size;
> +
> +                       here->e_value_offs = cpu_to_le16(min_offs - new_size);
>                         if (i->value == EXT4_ZERO_XATTR_VALUE) {
> -                               memset(val, 0, size);
> +                               memset(val, 0, new_size);
>                         } else {
> -                               /* Clear the pad bytes first. */
> -                               memset(val + size - EXT4_XATTR_PAD, 0,
> -                                      EXT4_XATTR_PAD);
>                                 memcpy(val, i->value, i->value_len);
> +                               /* Clear padding bytes. */
> +                               memset(val + i->value_len, 0,
> +                                      new_size - i->value_len);
>                         }
>                 }
> -               s->here->e_value_size = cpu_to_le32(i->value_len);
> +               here->e_value_size = cpu_to_le32(i->value_len);
>         }
> -
> +       ret = 0;
>  out:
> -       return rc;
> +       iput(old_ea_inode);
> +       iput(new_ea_inode);
> +       return ret;
>  }
>
>  struct ext4_xattr_block_find {
> @@ -1224,6 +1642,8 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
>         struct mb_cache_entry *ce = NULL;
>         int error = 0;
>         struct mb_cache *ext4_mb_cache = EXT4_GET_MB_CACHE(inode);
> +       struct inode *ea_inode = NULL;
> +       size_t old_ea_inode_size = 0;
>
>  #define header(x) ((struct ext4_xattr_header *)(x))
>
> @@ -1278,6 +1698,24 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
>                         header(s->base)->h_refcount = cpu_to_le32(1);
>                         s->here = ENTRY(s->base + offset);
>                         s->end = s->base + bs->bh->b_size;
> +
> +                       /*
> +                        * If existing entry points to an xattr inode, we need
> +                        * to prevent ext4_xattr_set_entry() from decrementing
> +                        * ref count on it because the reference belongs to the
> +                        * original block. In this case, make the entry look
> +                        * like it has an empty value.
> +                        */
> +                       if (!s->not_found && s->here->e_value_inum) {
> +                               /*
> +                                * Defer quota free call for previous inode
> +                                * until success is guaranteed.
> +                                */
> +                               old_ea_inode_size = le32_to_cpu(
> +                                                       s->here->e_value_size);
> +                               s->here->e_value_inum = 0;
> +                               s->here->e_value_size = 0;
> +                       }
>                 }
>         } else {
>                 /* Allocate a buffer where we construct the new block. */
> @@ -1299,6 +1737,24 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
>                 goto bad_block;
>         if (error)
>                 goto cleanup;
> +
> +       if (i->value && s->here->e_value_inum) {
> +               unsigned int ea_ino;
> +
> +               /*
> +                * A ref count on ea_inode has been taken as part of the call to
> +                * ext4_xattr_set_entry() above. We would like to drop this
> +                * extra ref but we have to wait until the xattr block is
> +                * initialized and has its own ref count on the ea_inode.
> +                */
> +               ea_ino = le32_to_cpu(s->here->e_value_inum);
> +               error = ext4_xattr_inode_iget(inode, ea_ino, &ea_inode);
> +               if (error) {
> +                       ea_inode = NULL;
> +                       goto cleanup;
> +               }
> +       }
> +
>         if (!IS_LAST_ENTRY(s->first))
>                 ext4_xattr_rehash(header(s->base), s->here);
>
> @@ -1409,6 +1865,22 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
>                                                  EXT4_FREE_BLOCKS_METADATA);
>                                 goto cleanup;
>                         }
> +                       error = ext4_xattr_inode_inc_ref_all(handle, inode,
> +                                                     ENTRY(header(s->base)+1));
> +                       if (error)
> +                               goto getblk_failed;
> +                       if (ea_inode) {
> +                               /* Drop the extra ref on ea_inode. */
> +                               error = ext4_xattr_inode_dec_ref(handle,
> +                                                                ea_inode);
> +                               if (error)
> +                                       ext4_warning_inode(ea_inode,
> +                                                          "dec ref error=%d",
> +                                                          error);
> +                               iput(ea_inode);
> +                               ea_inode = NULL;
> +                       }
> +
>                         lock_buffer(new_bh);
>                         error = ext4_journal_get_create_access(handle, new_bh);
>                         if (error) {
> @@ -1428,15 +1900,38 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
>                 }
>         }
>
> +       if (old_ea_inode_size)
> +               ext4_xattr_inode_free_quota(inode, old_ea_inode_size);
> +
>         /* Update the inode. */
>         EXT4_I(inode)->i_file_acl = new_bh ? new_bh->b_blocknr : 0;
>
>         /* Drop the previous xattr block. */
> -       if (bs->bh && bs->bh != new_bh)
> -               ext4_xattr_release_block(handle, inode, bs->bh);
> +       if (bs->bh && bs->bh != new_bh) {
> +               struct ext4_xattr_inode_array *ea_inode_array = NULL;
> +
> +               ext4_xattr_release_block(handle, inode, bs->bh,
> +                                        &ea_inode_array,
> +                                        0 /* extra_credits */);
> +               ext4_xattr_inode_array_free(ea_inode_array);
> +       }
>         error = 0;
>
>  cleanup:
> +       if (ea_inode) {
> +               int error2;
> +
> +               error2 = ext4_xattr_inode_dec_ref(handle, ea_inode);
> +               if (error2)
> +                       ext4_warning_inode(ea_inode, "dec ref error=%d",
> +                                          error2);
> +
> +               /* If there was an error, revert the quota charge. */
> +               if (error)
> +                       ext4_xattr_inode_free_quota(inode,
> +                                                   i_size_read(ea_inode));
> +               iput(ea_inode);
> +       }
>         if (ce)
>                 mb_cache_entry_put(ext4_mb_cache, ce);
>         brelse(new_bh);
> @@ -1561,6 +2056,22 @@ static int ext4_xattr_value_same(struct ext4_xattr_search *s,
>         return !memcmp(value, i->value, i->value_len);
>  }
>
> +static struct buffer_head *ext4_xattr_get_block(struct inode *inode)
> +{
> +       struct buffer_head *bh;
> +       int error;
> +
> +       if (!EXT4_I(inode)->i_file_acl)
> +               return NULL;
> +       bh = sb_bread(inode->i_sb, EXT4_I(inode)->i_file_acl);
> +       if (!bh)
> +               return ERR_PTR(-EIO);
> +       error = ext4_xattr_check_block(inode, bh);
> +       if (error)
> +               return ERR_PTR(error);
> +       return bh;
> +}
> +
>  /*
>   * ext4_xattr_set_handle()
>   *
> @@ -1603,9 +2114,18 @@ ext4_xattr_set_handle(handle_t *handle, struct inode *inode, int name_index,
>
>         /* Check journal credits under write lock. */
>         if (ext4_handle_valid(handle)) {
> +               struct buffer_head *bh;
>                 int credits;
>
> -               credits = ext4_xattr_set_credits(inode, value_len);
> +               bh = ext4_xattr_get_block(inode);
> +               if (IS_ERR(bh)) {
> +                       error = PTR_ERR(bh);
> +                       goto cleanup;
> +               }
> +
> +               credits = __ext4_xattr_set_credits(inode->i_sb, bh, value_len);
> +               brelse(bh);
> +
>                 if (!ext4_handle_has_enough_credits(handle, credits)) {
>                         error = -ENOSPC;
>                         goto cleanup;
> @@ -1641,6 +2161,7 @@ ext4_xattr_set_handle(handle_t *handle, struct inode *inode, int name_index,
>                 if (flags & XATTR_CREATE)
>                         goto cleanup;
>         }
> +
>         if (!value) {
>                 if (!is.s.not_found)
>                         error = ext4_xattr_ibody_set(handle, inode, &i, &is);
> @@ -1709,34 +2230,29 @@ ext4_xattr_set_handle(handle_t *handle, struct inode *inode, int name_index,
>         return error;
>  }
>
> -int ext4_xattr_set_credits(struct inode *inode, size_t value_len)
> +int ext4_xattr_set_credits(struct inode *inode, size_t value_len, int *credits)
>  {
> -       struct super_block *sb = inode->i_sb;
> -       int credits;
> -
> -       if (!EXT4_SB(sb)->s_journal)
> -               return 0;
> +       struct buffer_head *bh;
> +       int err;
>
> -       credits = EXT4_DATA_TRANS_BLOCKS(inode->i_sb);
> +       *credits = 0;
>
> -       /*
> -        * In case of inline data, we may push out the data to a block,
> -        * so we need to reserve credits for this eventuality
> -        */
> -       if (ext4_has_inline_data(inode))
> -               credits += ext4_writepage_trans_blocks(inode) + 1;
> -
> -       if (ext4_has_feature_ea_inode(sb)) {
> -               int nrblocks = (value_len + sb->s_blocksize - 1) >>
> -                                       sb->s_blocksize_bits;
> +       if (!EXT4_SB(inode->i_sb)->s_journal)
> +               return 0;
>
> -               /* For new inode */
> -               credits += EXT4_SINGLEDATA_TRANS_BLOCKS(sb) + 3;
> +       down_read(&EXT4_I(inode)->xattr_sem);
>
> -               /* For data blocks of EA inode */
> -               credits += ext4_meta_trans_blocks(inode, nrblocks, 0);
> +       bh = ext4_xattr_get_block(inode);
> +       if (IS_ERR(bh)) {
> +               err = PTR_ERR(bh);
> +       } else {
> +               *credits = __ext4_xattr_set_credits(inode->i_sb, bh, value_len);
> +               brelse(bh);
> +               err = 0;
>         }
> -       return credits;
> +
> +       up_read(&EXT4_I(inode)->xattr_sem);
> +       return err;
>  }
>
>  /*
> @@ -1761,7 +2277,10 @@ ext4_xattr_set(struct inode *inode, int name_index, const char *name,
>                 return error;
>
>  retry:
> -       credits = ext4_xattr_set_credits(inode, value_len);
> +       error = ext4_xattr_set_credits(inode, value_len, &credits);
> +       if (error)
> +               return error;
> +
>         handle = ext4_journal_start(inode, EXT4_HT_XATTR, credits);
>         if (IS_ERR(handle)) {
>                 error = PTR_ERR(handle);
> @@ -2067,10 +2586,10 @@ int ext4_expand_extra_isize_ea(struct inode *inode, int new_extra_isize,
>         return error;
>  }
>
> -
>  #define EIA_INCR 16 /* must be 2^n */
>  #define EIA_MASK (EIA_INCR - 1)
> -/* Add the large xattr @inode into @ea_inode_array for later deletion.
> +
> +/* Add the large xattr @inode into @ea_inode_array for deferred iput().
>   * If @ea_inode_array is new or full it will be grown and the old
>   * contents copied over.
>   */
> @@ -2115,21 +2634,19 @@ ext4_expand_inode_array(struct ext4_xattr_inode_array **ea_inode_array,
>   * ext4_xattr_delete_inode()
>   *
>   * Free extended attribute resources associated with this inode. Traverse
> - * all entries and unlink any xattr inodes associated with this inode. This
> - * is called immediately before an inode is freed. We have exclusive
> - * access to the inode. If an orphan inode is deleted it will also delete any
> - * xattr block and all xattr inodes. They are checked by ext4_xattr_inode_iget()
> - * to ensure they belong to the parent inode and were not deleted already.
> + * all entries and decrement reference on any xattr inodes associated with this
> + * inode. This is called immediately before an inode is freed. We have exclusive
> + * access to the inode. If an orphan inode is deleted it will also release its
> + * references on xattr block and xattr inodes.
>   */
> -int
> -ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
> -                       struct ext4_xattr_inode_array **ea_inode_array,
> -                       int extra_credits)
> +int ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
> +                           struct ext4_xattr_inode_array **ea_inode_array,
> +                           int extra_credits)
>  {
>         struct buffer_head *bh = NULL;
>         struct ext4_xattr_ibody_header *header;
> -       struct ext4_inode *raw_inode;
>         struct ext4_iloc iloc = { .bh = NULL };
> +       struct ext4_xattr_entry *entry;
>         int error;
>
>         error = ext4_xattr_ensure_credits(handle, inode, extra_credits,
> @@ -2141,66 +2658,71 @@ ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
>                 goto cleanup;
>         }
>
> -       if (!ext4_test_inode_state(inode, EXT4_STATE_XATTR))
> -               goto delete_external_ea;
> +       if (ext4_has_feature_ea_inode(inode->i_sb) &&
> +           ext4_test_inode_state(inode, EXT4_STATE_XATTR)) {
>
> -       error = ext4_get_inode_loc(inode, &iloc);
> -       if (error)
> -               goto cleanup;
> -
> -       error = ext4_journal_get_write_access(handle, iloc.bh);
> -       if (error)
> -               goto cleanup;
> +               error = ext4_get_inode_loc(inode, &iloc);
> +               if (error) {
> +                       EXT4_ERROR_INODE(inode, "inode loc (error %d)", error);
> +                       goto cleanup;
> +               }
>
> -       raw_inode = ext4_raw_inode(&iloc);
> -       header = IHDR(inode, raw_inode);
> -       ext4_xattr_inode_remove_all(handle, inode, iloc.bh, IFIRST(header),
> -                                   false /* block_csum */, ea_inode_array,
> -                                   extra_credits);
> +               error = ext4_journal_get_write_access(handle, iloc.bh);
> +               if (error) {
> +                       EXT4_ERROR_INODE(inode, "write access (error %d)",
> +                                        error);
> +                       goto cleanup;
> +               }
>
> -delete_external_ea:
> -       if (!EXT4_I(inode)->i_file_acl) {
> -               error = 0;
> -               goto cleanup;
> -       }
> -       bh = sb_bread(inode->i_sb, EXT4_I(inode)->i_file_acl);
> -       if (!bh) {
> -               EXT4_ERROR_INODE(inode, "block %llu read error",
> -                                EXT4_I(inode)->i_file_acl);
> -               error = -EIO;
> -               goto cleanup;
> -       }
> -       if (BHDR(bh)->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC) ||
> -           BHDR(bh)->h_blocks != cpu_to_le32(1)) {
> -               EXT4_ERROR_INODE(inode, "bad block %llu",
> -                                EXT4_I(inode)->i_file_acl);
> -               error = -EFSCORRUPTED;
> -               goto cleanup;
> +               header = IHDR(inode, ext4_raw_inode(&iloc));
> +               if (header->h_magic == cpu_to_le32(EXT4_XATTR_MAGIC))
> +                       ext4_xattr_inode_dec_ref_all(handle, inode, iloc.bh,
> +                                                    IFIRST(header),
> +                                                    false /* block_csum */,
> +                                                    ea_inode_array,
> +                                                    extra_credits,
> +                                                    false /* skip_quota */);
>         }
>
> -       if (ext4_has_feature_ea_inode(inode->i_sb)) {
> -               error = ext4_journal_get_write_access(handle, bh);
> -               if (error) {
> -                       EXT4_ERROR_INODE(inode, "write access %llu",
> +       if (EXT4_I(inode)->i_file_acl) {
> +               bh = sb_bread(inode->i_sb, EXT4_I(inode)->i_file_acl);
> +               if (!bh) {
> +                       EXT4_ERROR_INODE(inode, "block %llu read error",
>                                          EXT4_I(inode)->i_file_acl);
> +                       error = -EIO;
> +                       goto cleanup;
> +               }
> +               error = ext4_xattr_check_block(inode, bh);
> +               if (error) {
> +                       EXT4_ERROR_INODE(inode, "bad block %llu (error %d)",
> +                                        EXT4_I(inode)->i_file_acl, error);
>                         goto cleanup;
>                 }
> -               ext4_xattr_inode_remove_all(handle, inode, bh,
> -                                           BFIRST(bh),
> -                                           true /* block_csum */,
> -                                           ea_inode_array,
> -                                           extra_credits);
> -       }
>
> -       ext4_xattr_release_block(handle, inode, bh);
> -       /* Update i_file_acl within the same transaction that releases block. */
> -       EXT4_I(inode)->i_file_acl = 0;
> -       error = ext4_mark_inode_dirty(handle, inode);
> -       if (error) {
> -               EXT4_ERROR_INODE(inode, "mark inode dirty (error %d)",
> -                                error);
> -               goto cleanup;
> +               if (ext4_has_feature_ea_inode(inode->i_sb)) {
> +                       for (entry = BFIRST(bh); !IS_LAST_ENTRY(entry);
> +                            entry = EXT4_XATTR_NEXT(entry))
> +                               if (entry->e_value_inum)
> +                                       ext4_xattr_inode_free_quota(inode,
> +                                             le32_to_cpu(entry->e_value_size));
> +
> +               }
> +
> +               ext4_xattr_release_block(handle, inode, bh, ea_inode_array,
> +                                        extra_credits);
> +               /*
> +                * Update i_file_acl value in the same transaction that releases
> +                * block.
> +                */
> +               EXT4_I(inode)->i_file_acl = 0;
> +               error = ext4_mark_inode_dirty(handle, inode);
> +               if (error) {
> +                       EXT4_ERROR_INODE(inode, "mark inode dirty (error %d)",
> +                                        error);
> +                       goto cleanup;
> +               }
>         }
> +       error = 0;
>  cleanup:
>         brelse(iloc.bh);
>         brelse(bh);
> @@ -2209,17 +2731,13 @@ ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
>
>  void ext4_xattr_inode_array_free(struct ext4_xattr_inode_array *ea_inode_array)
>  {
> -       struct inode    *ea_inode;
> -       int             idx = 0;
> +       int idx;
>
>         if (ea_inode_array == NULL)
>                 return;
>
> -       for (; idx < ea_inode_array->count; ++idx) {
> -               ea_inode = ea_inode_array->inodes[idx];
> -               clear_nlink(ea_inode);
> -               iput(ea_inode);
> -       }
> +       for (idx = 0; idx < ea_inode_array->count; ++idx)
> +               iput(ea_inode_array->inodes[idx]);
>         kfree(ea_inode_array);
>  }
>
> diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
> index b2005a2716d9..67616cb9a059 100644
> --- a/fs/ext4/xattr.h
> +++ b/fs/ext4/xattr.h
> @@ -69,19 +69,6 @@ struct ext4_xattr_entry {
>                 EXT4_I(inode)->i_extra_isize))
>  #define IFIRST(hdr) ((struct ext4_xattr_entry *)((hdr)+1))
>
> -/*
> - * Link EA inode back to parent one using i_mtime field.
> - * Extra integer type conversion added to ignore higher
> - * bits in i_mtime.tv_sec which might be set by ext4_get()
> - */
> -#define EXT4_XATTR_INODE_SET_PARENT(inode, inum)      \
> -do {                                                  \
> -      (inode)->i_mtime.tv_sec = inum;                 \
> -} while(0)
> -
> -#define EXT4_XATTR_INODE_GET_PARENT(inode)            \
> -((__u32)(inode)->i_mtime.tv_sec)
> -
>  /*
>   * The minimum size of EA value when you start storing it in an external inode
>   * size of block - size of header - size of 1 entry - 4 null bytes
> @@ -165,9 +152,9 @@ extern ssize_t ext4_listxattr(struct dentry *, char *, size_t);
>  extern int ext4_xattr_get(struct inode *, int, const char *, void *, size_t);
>  extern int ext4_xattr_set(struct inode *, int, const char *, const void *, size_t, int);
>  extern int ext4_xattr_set_handle(handle_t *, struct inode *, int, const char *, const void *, size_t, int);
> -extern int ext4_xattr_set_credits(struct inode *inode, size_t value_len);
> +extern int ext4_xattr_set_credits(struct inode *inode, size_t value_len,
> +                                 int *credits);
>
> -extern int ext4_xattr_inode_unlink(struct inode *inode, unsigned long ea_ino);
>  extern int ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
>                                    struct ext4_xattr_inode_array **array,
>                                    int extra_credits);
> diff --git a/fs/mbcache.c b/fs/mbcache.c
> index 45a8d52dc991..d818fd236787 100644
> --- a/fs/mbcache.c
> +++ b/fs/mbcache.c
> @@ -13,10 +13,11 @@
>   * mb_cache_entry_delete()).
>   *
>   * Ext2 and ext4 use this cache for deduplication of extended attribute blocks.
> - * They use hash of a block contents as a key and block number as a value.
> - * That's why keys need not be unique (different xattr blocks may end up having
> - * the same hash). However block number always uniquely identifies a cache
> - * entry.
> + * Ext4 also uses it for deduplication of xattr values stored in inodes.
> + * They use hash of data as a key and provide a value that may represent a
> + * block or inode number. That's why keys need not be unique (hash of different
> + * data may be the same). However user provided value always uniquely
> + * identifies a cache entry.
>   *
>   * We provide functions for creation and removal of entries, search by key,
>   * and a special "delete entry with given key-value pair" operation. Fixed
> --
> 2.13.1.518.g3df882009-goog
>




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