Because we can badly over-reserve metadata when we
calculate worst-case, it complicates things for quota, since
we must reserve and then claim later, retry on EDQUOT, etc.
Quota is also a generally smaller pool than fs free blocks,
so this over-reservation hurts more, and more often.
I'm of the opinion that it's not the worst thing to allow
metadata to push a user slightly over quota, if we can simplify
the code by doing so.
The patch below stops the speculative quota-charging for
worst-case metadata requirements, and just charges quota
when the blocks are allocated at writeout. It also is
able to remove the try-again loop on EDQUOT.
In the longer run I'd like to even consider not charging
speculative metadata against the superblock counters, and use
a reserved space pool similar to what XFS does, but this change
could maybe stand on its own, too.
Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
---
balloc.c | 5 +++--
inode.c | 63 +++++++++++++++++++++------------------------------------------
2 files changed, 24 insertions(+), 44 deletions(-)
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 22bc743..e11e5b0 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -604,13 +604,14 @@ ext4_fsblk_t ext4_new_meta_blocks(handle_t *handle, struct inode *inode,
ret = ext4_mb_new_blocks(handle, &ar, errp);
if (count)
*count = ar.len;
-
/*
- * Account for the allocated meta blocks
+ * Account for the allocated meta blocks. We will never
+ * fail EDQUOT for metdata, but we do account for it.
*/
if (!(*errp) && EXT4_I(inode)->i_delalloc_reserved_flag) {
spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
EXT4_I(inode)->i_allocated_meta_blocks += ar.len;
+ vfs_dq_alloc_block(inode, ar.len);
spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
}
return ret;
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index e119524..6f0faf0 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1058,7 +1058,6 @@ void ext4_da_update_reserve_space(struct inode *inode,
{
struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
struct ext4_inode_info *ei = EXT4_I(inode);
- int mdb_free = 0, allocated_meta_blocks = 0;
spin_lock(&ei->i_block_reservation_lock);
if (unlikely(used > ei->i_reserved_data_blocks)) {
@@ -1072,11 +1071,10 @@ void ext4_da_update_reserve_space(struct inode *inode,
/* Update per-inode reservations */
ei->i_reserved_data_blocks -= used;
- used += ei->i_allocated_meta_blocks;
ei->i_reserved_meta_blocks -= ei->i_allocated_meta_blocks;
- allocated_meta_blocks = ei->i_allocated_meta_blocks;
+ percpu_counter_sub(&sbi->s_dirtyblocks_counter,
+ used + ei->i_allocated_meta_blocks);
ei->i_allocated_meta_blocks = 0;
- percpu_counter_sub(&sbi->s_dirtyblocks_counter, used);
if (ei->i_reserved_data_blocks == 0) {
/*
@@ -1084,30 +1082,23 @@ void ext4_da_update_reserve_space(struct inode *inode,
* only when we have written all of the delayed
* allocation blocks.
*/
- mdb_free = ei->i_reserved_meta_blocks;
+ percpu_counter_sub(&sbi->s_dirtyblocks_counter,
+ ei->i_reserved_meta_blocks);
ei->i_reserved_meta_blocks = 0;
ei->i_da_metadata_calc_len = 0;
- percpu_counter_sub(&sbi->s_dirtyblocks_counter, mdb_free);
}
spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
- /* Update quota subsystem */
+ /* Update quota subsystem for data blocks */
if (quota_claim) {
vfs_dq_claim_block(inode, used);
- if (mdb_free)
- vfs_dq_release_reservation_block(inode, mdb_free);
} else {
/*
* We did fallocate with an offset that is already delayed
* allocated. So on delayed allocated writeback we should
- * not update the quota for allocated blocks. But then
- * converting an fallocate region to initialized region would
- * have caused a metadata allocation. So claim quota for
- * that
+ * not re-claim the quota for fallocated blocks.
*/
- if (allocated_meta_blocks)
- vfs_dq_claim_block(inode, allocated_meta_blocks);
- vfs_dq_release_reservation_block(inode, mdb_free + used);
+ vfs_dq_release_reservation_block(inode, used);
}
/*
@@ -1835,7 +1826,7 @@ static int ext4_da_reserve_space(struct inode *inode, sector_t lblock)
int retries = 0;
struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
struct ext4_inode_info *ei = EXT4_I(inode);
- unsigned long md_needed, md_reserved;
+ unsigned long md_needed;
/*
* recalculate the amount of metadata blocks to reserve
@@ -1844,20 +1835,23 @@ static int ext4_da_reserve_space(struct inode *inode, sector_t lblock)
*/
repeat:
spin_lock(&ei->i_block_reservation_lock);
- md_reserved = ei->i_reserved_meta_blocks;
md_needed = ext4_calc_metadata_amount(inode, lblock);
spin_unlock(&ei->i_block_reservation_lock);
/*
- * Make quota reservation here to prevent quota overflow
- * later. Real quota accounting is done at pages writeout
- * time.
+ * We will charge metadata quota at writeout time; this saves
+ * us from metadata over-estimation, though we may go over by
+ * a small amount in the end. Here we just reserve for data.
*/
- if (vfs_dq_reserve_block(inode, md_needed + 1))
+ if (vfs_dq_reserve_block(inode, 1))
return -EDQUOT;
+ /*
+ * We do still charge estimated metadata to the sb though;
+ * we cannot afford to run out of free blocks.
+ */
if (ext4_claim_free_blocks(sbi, md_needed + 1)) {
- vfs_dq_release_reservation_block(inode, md_needed + 1);
+ vfs_dq_release_reservation_block(inode, 1);
if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
yield();
goto repeat;
@@ -1904,12 +1898,13 @@ static void ext4_da_release_space(struct inode *inode, int to_free)
* only when we have written all of the delayed
* allocation blocks.
*/
- to_free += ei->i_reserved_meta_blocks;
+ percpu_counter_sub(&sbi->s_dirtyblocks_counter,
+ ei->i_reserved_meta_blocks);
ei->i_reserved_meta_blocks = 0;
ei->i_da_metadata_calc_len = 0;
}
- /* update fs dirty blocks counter */
+ /* update fs dirty data blocks counter */
percpu_counter_sub(&sbi->s_dirtyblocks_counter, to_free);
spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
@@ -3038,7 +3033,7 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata)
{
- int ret, retries = 0, quota_retries = 0;
+ int ret, retries = 0;
struct page *page;
pgoff_t index;
unsigned from, to;
@@ -3097,22 +3092,6 @@ retry:
if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
goto retry;
-
- if ((ret == -EDQUOT) &&
- EXT4_I(inode)->i_reserved_meta_blocks &&
- (quota_retries++ < 3)) {
- /*
- * Since we often over-estimate the number of meta
- * data blocks required, we may sometimes get a
- * spurios out of quota error even though there would
- * be enough space once we write the data blocks and
- * find out how many meta data blocks were _really_
- * required. So try forcing the inode write to see if
- * that helps.
- */
- write_inode_now(inode, (quota_retries == 3));
- goto retry;
- }
out:
return ret;
}
--
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