Hi Michael, // sorry for the delay...
On Mon, Dec 10, 2007 at 06:02:55PM -0800, Michael Rubin wrote: > From: Michael Rubin <[EMAIL PROTECTED]> > > Fixing a bug where writing to large files while concurrently writing to > smaller ones creates a situation where writeback cannot keep up with the > traffic and memory baloons until the we hit the threshold watermark. This > can result in surprising latency spikes when syncing. This latency > can take minutes on large memory systems. Upon request I can provide > a test to reproduce this situation. > > The only concern I have is that this makes the wb_kupdate slightly more > agressive. I am not sure it is enough to cause any problems. I think > there is enough checks to throttle the background activity. > > Feng also the one line change that you recommended here > http://marc.info/?l=linux-kernel&m=119629655402153&w=2 had no effect. > > Signed-off-by: Michael Rubin <[EMAIL PROTECTED]> > --- > Index: 2624rc3_feng/fs/fs-writeback.c > =================================================================== > --- 2624rc3_feng.orig/fs/fs-writeback.c 2007-11-29 14:44:24.000000000 > -0800 > +++ 2624rc3_feng/fs/fs-writeback.c 2007-12-10 17:21:45.000000000 -0800 > @@ -408,8 +408,7 @@ sync_sb_inodes(struct super_block *sb, s > { > const unsigned long start = jiffies; /* livelock avoidance */ > > - if (!wbc->for_kupdate || list_empty(&sb->s_io)) > - queue_io(sb, wbc->older_than_this); > + queue_io(sb, wbc->older_than_this); Basically it's a workaround by changing the service priority. Assume A to be the large file and B,C,D,E,... to be the small files. - old behavior: sync 4MB of A; sync B,C; congestion_wait(); sync 4MB of A; sync D,E; congestion_wait(); sync 4MB of A; sync F,G; congestion_wait(); ... - new behavior: sync 4MB of A; sync 4MB of A; sync 4MB of A; sync 4MB of A; sync 4MB of A; ... // repeat until A is clean sync B,C,D,E,F,G; So the bug is gone, but now A could possibly starve other files :-( > while (!list_empty(&sb->s_io)) { > struct inode *inode = list_entry(sb->s_io.prev, > Index: 2624rc3_feng/mm/page-writeback.c > =================================================================== > --- 2624rc3_feng.orig/mm/page-writeback.c 2007-11-16 21:16:36.000000000 > -0800 > +++ 2624rc3_feng/mm/page-writeback.c 2007-12-10 17:37:17.000000000 -0800 > @@ -638,7 +638,7 @@ static void wb_kupdate(unsigned long arg > wbc.nr_to_write = MAX_WRITEBACK_PAGES; > writeback_inodes(&wbc); > if (wbc.nr_to_write > 0) { > - if (wbc.encountered_congestion || wbc.more_io) > + if (wbc.encountered_congestion) No, this could make wb_kupdate() abort even when there are more data to be synced. That will make David Chinner unhappy ;-) > congestion_wait(WRITE, HZ/10); > else > break; /* All the old data is written */ Just a minute, I'll propose a way out of this bug :-) Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
