From 2e6883bdf49abd0e7f0d9b6297fc3be7ebb2250b Mon Sep 17 00:00:00 2001 From: Fengguang Wu Date: Tue, 16 Oct 2007 23:30:43 -0700 Subject: writeback: introduce writeback_control.more_io to indicate more io After making dirty a 100M file, the normal behavior is to start the writeback for all data after 30s delays. But sometimes the following happens instead: - after 30s: ~4M - after 5s: ~4M - after 5s: all remaining 92M Some analyze shows that the internal io dispatch queues goes like this: s_io s_more_io ------------------------- 1) 100M,1K 0 2) 1K 96M 3) 0 96M 1) initial state with a 100M file and a 1K file 2) 4M written, nr_to_write <= 0, so write more 3) 1K written, nr_to_write > 0, no more writes(BUG) nr_to_write > 0 in (3) fools the upper layer to think that data have all been written out. The big dirty file is actually still sitting in s_more_io. We cannot simply splice s_more_io back to s_io as soon as s_io becomes empty, and let the loop in generic_sync_sb_inodes() continue: this may starve newly expired inodes in s_dirty. It is also not an option to draw inodes from both s_more_io and s_dirty, an let the loop go on: this might lead to live locks, and might also starve other superblocks in sync time(well kupdate may still starve some superblocks, that's another bug). We have to return when a full scan of s_io completes. So nr_to_write > 0 does not necessarily mean that "all data are written". This patch introduces a flag writeback_control.more_io to indicate this situation. With it the big dirty file no longer has to wait for the next kupdate invocation 5s later. Cc: David Chinner Cc: Ken Chen Signed-off-by: Fengguang Wu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/fs-writeback.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 414df43706c7..71c158ac60a3 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -473,6 +473,8 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc) if (wbc->nr_to_write <= 0) break; } + if (!list_empty(&sb->s_more_io)) + wbc->more_io = 1; return; /* Leave any unwritten inodes on s_io */ } -- cgit v1.2.2