From 10542c229a4e8e25b40357beea66abe9dacda2c0 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 4 Mar 2014 10:50:50 -0500 Subject: ext4: Speedup WB_SYNC_ALL pass called from sync(2) When doing filesystem wide sync, there's no need to force transaction commit (or synchronously write inode buffer) separately for each inode because ext4_sync_fs() takes care of forcing commit at the end (VFS takes care of flushing buffer cache, respectively). Most of the time this slowness doesn't manifest because previous WB_SYNC_NONE writeback doesn't leave much to write but when there are processes aggressively creating new files and several filesystems to sync, the sync slowness can be noticeable. In the following test script sync(1) takes around 6 minutes when there are two ext4 filesystems mounted on a standard SATA drive. After this patch sync takes a couple of seconds so we have about two orders of magnitude improvement. 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 Signed-off-by: Jan Kara Signed-off-by: "Theodore Ts'o" --- fs/ext4/inode.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) (limited to 'fs/ext4') diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 5324a38d848d..ab3e8357929d 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -4455,7 +4455,12 @@ int ext4_write_inode(struct inode *inode, struct writeback_control *wbc) return -EIO; } - if (wbc->sync_mode != WB_SYNC_ALL) + /* + * No need to force transaction in WB_SYNC_NONE mode. Also + * ext4_sync_fs() will force the commit after everything is + * written. + */ + if (wbc->sync_mode != WB_SYNC_ALL || wbc->for_sync) return 0; err = ext4_force_commit(inode->i_sb); @@ -4465,7 +4470,11 @@ int ext4_write_inode(struct inode *inode, struct writeback_control *wbc) err = __ext4_get_inode_loc(inode, &iloc, 0); if (err) return err; - if (wbc->sync_mode == WB_SYNC_ALL) + /* + * sync(2) will flush the whole buffer cache. No need to do + * it here separately for each inode. + */ + if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) sync_dirty_buffer(iloc.bh); if (buffer_req(iloc.bh) && !buffer_uptodate(iloc.bh)) { EXT4_ERROR_INODE_BLOCK(inode, iloc.bh->b_blocknr, -- cgit v1.2.3