From c8afb44682fcef6273e8b8eb19fab13ddd05b386 Mon Sep 17 00:00:00 2001 From: Eric Sandeen Date: Wed, 23 Dec 2009 07:58:12 -0500 Subject: [PATCH] ext4: flush delalloc blocks when space is low 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 Signed-off-by: "Theodore Ts'o" --- fs/ext4/inode.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index ab80796..282621f 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2993,11 +2993,18 @@ 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; } -- 1.8.2.3