From c4a391b53a72d2df4ee97f96f78c1d5971b47489 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 12 Nov 2013 15:07:51 -0800 Subject: writeback: do not sync data dirtied after sync start When there are processes heavily creating small files while sync(2) is running, it can easily happen that quite some new files are created between WB_SYNC_NONE and WB_SYNC_ALL pass of sync(2). That can happen especially if there are several busy filesystems (remember that sync traverses filesystems sequentially and waits in WB_SYNC_ALL phase on one fs before starting it on another fs). Because WB_SYNC_ALL pass is slow (e.g. causes a transaction commit and cache flush for each inode in ext3), resulting sync(2) times are rather large. The following script reproduces the problem: function run_writers { for (( i = 0; i < 10; i++ )); do mkdir $1/dir$i for (( j = 0; j < 40000; j++ )); do dd if=/dev/zero of=$1/dir$i/$j bs=4k count=4 &>/dev/null done & done } for dir in "$@"; do run_writers $dir done sleep 40 time sync Fix the problem by disregarding inodes dirtied after sync(2) was called in the WB_SYNC_ALL pass. To allow for this, sync_inodes_sb() now takes a time stamp when sync has started which is used for setting up work for flusher threads. To give some numbers, when above script is run on two ext4 filesystems on simple SATA drive, the average sync time from 10 runs is 267.549 seconds with standard deviation 104.799426. With the patched kernel, the average sync time from 10 runs is 2.995 seconds with standard deviation 0.096. Signed-off-by: Jan Kara Reviewed-by: Fengguang Wu Reviewed-by: Dave Chinner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/xfs/xfs_super.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/xfs') diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c index 15188cc99449..8968f5036fa1 100644 --- a/fs/xfs/xfs_super.c +++ b/fs/xfs/xfs_super.c @@ -918,7 +918,7 @@ xfs_flush_inodes( struct super_block *sb = mp->m_super; if (down_read_trylock(&sb->s_umount)) { - sync_inodes_sb(sb); + sync_inodes_sb(sb, jiffies); up_read(&sb->s_umount); } } -- cgit v1.2.3