From: Andrew Morton Date: Wed, 17 Oct 2007 06:30:37 +0000 (-0700) Subject: writeback: fix time ordering of the per superblock dirty inode lists 6 X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=65cb9b47e0ea568a7a38cce7773052a6ea093629;p=GitHub%2FLineageOS%2Fandroid_kernel_samsung_universal7580.git writeback: fix time ordering of the per superblock dirty inode lists 6 Recycling the previous changelog: When the writeback function is operating in writeback-for-flushing mode (as opposed to writeback-for-integrity) and it encounters an I_LOCKed inode, it will skip writing that inode. This is done for throughput and latency: move on to another inode rather than blocking for this one. Writeback skips this inode by moving it off s_io and onto s_dirty, so that writeback can proceed with the other inodes on s_io. However that inode movement can corrupt s_dirty's reverse-time-orderedness. Fix that by using the new redirty_tail(), which will update the refiled inode's dirtied_when field. Note: the behaviour in here is a bit rude: if kupdate happens to come across a locked inode then it will defer writeback of that inode for another 30 seconds. We'll address that in the next patch. Address that here. What we do is to move the skipped inode to the _head_ of s_dirty, immediately eligible for writeout again. Instead of deferring that writeout for another 30 seconds. One would think that this might cause a livelock: we keep on trying to write the same locked inode. But it won't because: a) if that was the case, it would _already_ be happening on the balance_dirty_pages codepath. Because balance_dirty_pages() doesn't care about inode timestamps. b) if we skipped this inode then we won't have done any writeback. The higher-level writeback paths will see that wbc.nr_to_write didn't change and they'll then back off and take a nap. Cc: Mike Waychison Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 1b43cc9d9eb..30d9383c87c 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -308,7 +308,14 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) struct address_space *mapping = inode->i_mapping; int ret; - redirty_tail(inode); + /* + * We're skipping this inode because it's locked, and we're not + * doing writeback-for-data-integrity. Move it to the head of + * s_dirty so that writeback can proceed with the other inodes + * on s_io. We'll have another go at writing back this inode + * when the s_dirty iodes get moved back onto s_io. + */ + redirty_head(inode); /* * Even if we don't actually write the inode itself here,