> Creating many small files in rapid succession on a small
> filesystem can lead to spurious ENOSPC; on a 104MB filesystem:
>
> for i in `seq 1 22500`; do
> echo -n > $SCRATCH_MNT/$i
> echo XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX > $SCRATCH_MNT/$i
> done
>
> leads to ENOSPC even though after a sync, 40% of the fs is free
> again.
>
> This is because we reserve worst-case metadata for delalloc writes,
> and when data is allocated that worst-case reservation is not
> usually needed.
>
> When freespace is low, kicking off an async writeback will start
> converting that worst-case space usage into something more realistic,
> almost always freeing up space to continue.
>
> This resolves the testcase for me, and survives all 4 generic
> ENOSPC tests in xfstests.
>
> We'll still need a hard synchronous sync to squeeze out the last bit,
> but this fixes things up to a large degree.
>
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
Looks good.
Acked-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 5c5bc5d..5b3f468 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3024,11 +3024,18 @@ static int ext4_nonda_switch(struct super_block *sb)
> if (2 * free_blocks < 3 * dirty_blocks ||
> free_blocks < (dirty_blocks + EXT4_FREEBLOCKS_WATERMARK)) {
> /*
> - * free block count is less that 150% of dirty blocks
> - * or free blocks is less that watermark
> + * free block count is less than 150% of dirty blocks
> + * or free blocks is less than watermark
> */
> return 1;
> }
> + /*
> + * Even if we don't switch but are nearing capacity,
> + * start pushing delalloc when 1/2 of free blocks are dirty.
> + */
> + if (free_blocks < 2 * dirty_blocks)
> + writeback_inodes_sb_if_idle(sb);
> +
> return 0;
> }
>
>
> --
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--
Jan Kara <jack@xxxxxxx>
SuSE CR Labs
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