在 2008-08-27三的 20:58 +0530，Aneesh Kumar K.V写道：
> With delayed allocation we need to make sure block are reserved
> before we attempt to allocate them. Otherwise we get block
> allocation failure (ENOSPC) during writepages which cannot
> be handled. This would mean silent data loss (We do a printk
> stating data will be lost). This patch update the DIO
> and fallocate code path to do block reservation before block
> allocation. This is needed to make sure parallel DIO and
> fallocate request doesn't take block out of delayed reserve
> space.
>
> When free blocks count go below a threshold we switch to
> a slow patch which looks at other CPU's accumulated percpu
> counter values.
>
Added this patch to patch queue.
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> ---
> fs/ext4/balloc.c | 58 ++++++++++++++++++++++++++++++++++++++--------------
> fs/ext4/ext4.h | 13 +++++++++++
> fs/ext4/inode.c | 5 +---
> fs/ext4/mballoc.c | 23 +++++++++++---------
> 4 files changed, 69 insertions(+), 30 deletions(-)
>
> diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
> index cfed283..dc10bfd 100644
> --- a/fs/ext4/balloc.c
> +++ b/fs/ext4/balloc.c
> @@ -1602,6 +1602,32 @@ ext4_try_to_allocate_with_rsv(struct super_block *sb, handle_t *handle,
> return ret;
> }
>
> +int ext4_claim_free_blocks(struct ext4_sb_info *sbi,
> + ext4_fsblk_t nblocks)
> +{
> + s64 free_blocks;
> + ext4_fsblk_t root_blocks = 0;
> + struct percpu_counter *fbc = &sbi->s_freeblocks_counter;
> +
> + free_blocks = percpu_counter_read(fbc);
> +
> + if (!capable(CAP_SYS_RESOURCE) &&
> + sbi->s_resuid != current->fsuid &&
> + (sbi->s_resgid == 0 || !in_group_p(sbi->s_resgid)))
> + root_blocks = ext4_r_blocks_count(sbi->s_es);
> +
> + if (free_blocks - (nblocks + root_blocks) < EXT4_FREEBLOCKS_WATERMARK)
> + free_blocks = percpu_counter_sum(&sbi->s_freeblocks_counter);
> +
> + if (free_blocks < (root_blocks + nblocks))
> + /* we don't have free space */
> + return -ENOSPC;
> +
> + /* reduce fs free blocks counter */
> + percpu_counter_sub(fbc, nblocks);
> + return 0;
> +}
> +
Any reason that we don't do percpu_counter_sum_and_sub() together? I
thought this fixed the parallel reservation race before.
> /**
> * ext4_has_free_blocks()
> * @sbi: in-core super block structure.
> @@ -1623,18 +1649,17 @@ ext4_fsblk_t ext4_has_free_blocks(struct ext4_sb_info *sbi,
> sbi->s_resuid != current->fsuid &&
> (sbi->s_resgid == 0 || !in_group_p(sbi->s_resgid)))
> root_blocks = ext4_r_blocks_count(sbi->s_es);
> -#ifdef CONFIG_SMP
> - if (free_blocks - root_blocks < FBC_BATCH)
> - free_blocks =
> - percpu_counter_sum(&sbi->s_freeblocks_counter);
> -#endif
> +
> + if (free_blocks - (nblocks + root_blocks) < EXT4_FREEBLOCKS_WATERMARK)
> + free_blocks = percpu_counter_sum_positive(&sbi->s_freeblocks_counter);
> +
> if (free_blocks <= root_blocks)
> /* we don't have free space */
> return 0;
> if (free_blocks - root_blocks < nblocks)
> return free_blocks - root_blocks;
> return nblocks;
> - }
> +}
>
>
> /**
> @@ -1713,14 +1738,11 @@ ext4_fsblk_t ext4_old_new_blocks(handle_t *handle, struct inode *inode,
> /*
> * With delalloc we already reserved the blocks
> */
> - *count = ext4_has_free_blocks(sbi, *count);
> - }
> - if (*count == 0) {
> - *errp = -ENOSPC;
> - return 0; /*return with ENOSPC error */
> + if (ext4_claim_free_blocks(sbi, *count)) {
> + *errp = -ENOSPC;
> + return 0; /*return with ENOSPC error */
> + }
> }
> - num = *count;
> -
> /*
> * Check quota for allocation of this block.
> */
> @@ -1915,9 +1937,13 @@ ext4_fsblk_t ext4_old_new_blocks(handle_t *handle, struct inode *inode,
> le16_add_cpu(&gdp->bg_free_blocks_count, -num);
> gdp->bg_checksum = ext4_group_desc_csum(sbi, group_no, gdp);
> spin_unlock(sb_bgl_lock(sbi, group_no));
> - if (!EXT4_I(inode)->i_delalloc_reserved_flag)
> - percpu_counter_sub(&sbi->s_freeblocks_counter, num);
> -
> + if (!EXT4_I(inode)->i_delalloc_reserved_flag && (*count != num)) {
> + /*
> + * we allocated less blocks than we
> + * claimed. Add the difference back.
> + */
> + percpu_counter_add(&sbi->s_freeblocks_counter, *count - num);
> + }
> if (sbi->s_log_groups_per_flex) {
> ext4_group_t flex_group = ext4_flex_group(sbi, group_no);
> spin_lock(sb_bgl_lock(sbi, flex_group));
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 7f11b25..71a4fde 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1047,6 +1047,8 @@ extern ext4_fsblk_t ext4_new_blocks(handle_t *handle, struct inode *inode,
> unsigned long *count, int *errp);
> extern ext4_fsblk_t ext4_old_new_blocks(handle_t *handle, struct inode *inode,
> ext4_fsblk_t goal, unsigned long *count, int *errp);
> +extern int ext4_claim_free_blocks(struct ext4_sb_info *sbi,
> + ext4_fsblk_t nblocks);
> extern ext4_fsblk_t ext4_has_free_blocks(struct ext4_sb_info *sbi,
> ext4_fsblk_t nblocks);
> extern void ext4_free_blocks (handle_t *handle, struct inode *inode,
> @@ -1295,6 +1297,17 @@ do { \
> __ext4_std_error((sb), __func__, (errno)); \
> } while (0)
>
> +#ifdef CONFIG_SMP
> +/* Each CPU can accumulate FBC_BATCH blocks in their local
> + * counters. So we need to make sure we have free blocks more
> + * than FBC_BATCH * nr_cpu_ids. Also add a window of 4 times.
> + */
> +#define EXT4_FREEBLOCKS_WATERMARK (4 * (FBC_BATCH * nr_cpu_ids))
> +#else
> +#define EXT4_FREEBLOCKS_WATERMARK 0
> +#endif
> +
> +
> /*
> * Inodes and files operations
> */
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 1c289c1..d965a05 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1537,13 +1537,10 @@ static int ext4_da_reserve_space(struct inode *inode, int nrblocks)
> md_needed = mdblocks - EXT4_I(inode)->i_reserved_meta_blocks;
> total = md_needed + nrblocks;
>
> - if (ext4_has_free_blocks(sbi, total) < total) {
> + if (ext4_claim_free_blocks(sbi, total)) {
> spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
> return -ENOSPC;
> }
> - /* reduce fs free blocks counter */
> - percpu_counter_sub(&sbi->s_freeblocks_counter, total);
> -
> EXT4_I(inode)->i_reserved_data_blocks += nrblocks;
> EXT4_I(inode)->i_reserved_meta_blocks = mdblocks;
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 82dd0e4..4404b46 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2977,9 +2977,15 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
> * at write_begin() time for delayed allocation
> * do not double accounting
> */
> - if (!(ac->ac_flags & EXT4_MB_DELALLOC_RESERVED))
> - percpu_counter_sub(&sbi->s_freeblocks_counter,
> - ac->ac_b_ex.fe_len);
> + if (!(ac->ac_flags & EXT4_MB_DELALLOC_RESERVED) &&
> + ac->ac_o_ex.fe_len != ac->ac_b_ex.fe_len) {
> + /*
> + * we allocated less blocks than we calimed
> + * Add the difference back
> + */
> + percpu_counter_add(&sbi->s_freeblocks_counter,
> + ac->ac_o_ex.fe_len - ac->ac_b_ex.fe_len);
> + }
>
> if (sbi->s_log_groups_per_flex) {
> ext4_group_t flex_group = ext4_flex_group(sbi,
> @@ -4391,14 +4397,11 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
> /*
> * With delalloc we already reserved the blocks
> */
> - ar->len = ext4_has_free_blocks(sbi, ar->len);
> - }
> -
> - if (ar->len == 0) {
> - *errp = -ENOSPC;
> - return 0;
> + if (ext4_claim_free_blocks(sbi, ar->len)) {
> + *errp = -ENOSPC;
> + return 0;
> + }
> }
> -
> while (ar->len && DQUOT_ALLOC_BLOCK(ar->inode, ar->len)) {
> ar->flags |= EXT4_MB_HINT_NOPREALLOC;
> ar->len--;
--
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