On Sat, Nov 06, 2010 at 10:55:48AM +0800, Wu Fengguang wrote: > [add CC to linux-mm list] > > On Sat, Nov 06, 2010 at 06:30:38AM +0800, Christoph Hellwig wrote: > > > + /* > > > + * In WB_SYNC_ALL mode, we just want to ignore nr_to_write as > > > + * we need to write everything and livelock avoidance is implemented > > > + * differently. > > > + */ > > > + if (wbc.sync_mode == WB_SYNC_NONE) > > > + write_chunk = MAX_WRITEBACK_PAGES; > > > + else > > > + write_chunk = LONG_MAX; > > Good catch! > > > > > I think it would be useful to elaborate here on how livelock avoidance > > is supposed to work. > > It's supposed to sync files in a big loop > > for each dirty inode > write_cache_pages() > (quickly) tag currently dirty pages > (maybe slowly) sync all tagged pages > > Ideally the loop should call write_cache_pages() _once_ for each inode. > At least this is the assumption made by commit f446daaea (mm: > implement writeback livelock avoidance using page tagging). The above scheme relies on the filesystems to not skip pages in WB_SYNC_ALL mode. It seems necessary to add an explicit check at least in the -mm tree. Thanks, Fengguang --- writeback: check skipped pages on WB_SYNC_ALL In WB_SYNC_ALL mode, filesystems are not expected to skip dirty pages on temporal lock contentions or non fatal errors, otherwise sync() will return without actually syncing the skipped pages. Add a check to catch possible redirty_page_for_writepage() callers that violate this expectation. Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> --- fs/fs-writeback.c | 1 + 1 file changed, 1 insertion(+) --- linux-next.orig/fs/fs-writeback.c 2010-11-07 00:20:43.000000000 +0800 +++ linux-next/fs/fs-writeback.c 2010-11-07 00:29:29.000000000 +0800 @@ -527,6 +527,7 @@ static int writeback_sb_inodes(struct su * buffers. Skip this inode for now. */ redirty_tail(inode); + WARN_ON_ONCE(wbc->sync_mode == WB_SYNC_ALL); } spin_unlock(&inode_lock); iput(inode); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>