On Wed, 9 Feb 2011 19:28:46 +0100 Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote: > On Wed, Feb 09, 2011 at 04:46:56PM +0000, Mel Gorman wrote: > > On Wed, Feb 09, 2011 at 04:46:06PM +0100, Johannes Weiner wrote: > > > Hi, > > > > > > I think this should fix the problem of processes getting stuck in > > > reclaim that has been reported several times. > > > > I don't think it's the only source but I'm basing this on seeing > > constant looping in balance_pgdat() and calling congestion_wait() a few > > weeks ago that I haven't rechecked since. However, this looks like a > > real fix for a real problem. > > Agreed. Just yesterday I spent some time on the lumpy compaction > changes after wondering about Michal's khugepaged 100% report, and I > expected some fix was needed in this area (as I couldn't find any bug > in khugepaged yet, so the lumpy compaction looked the next candidate > for bugs). > > I've also been wondering about the !nr_scanned check in > should_continue_reclaim too but I didn't look too much into the caller > (I was tempted to remove it all together). I don't see how checking > nr_scanned can be safe even after we fix the caller to avoid passing > non-zero values if "goto restart". > > nr_scanned is incremented even for !page_evictable... so it's not > really useful to insist, just because we scanned something, in my > view. It looks bogus... So my proposal would be below. > > ==== > Subject: mm: stop checking nr_scanned in should_continue_reclaim > > From: Andrea Arcangeli <aarcange@xxxxxxxxxx> > > nr_scanned is incremented even for !page_evictable... so it's not > really useful to insist, just because we scanned something. So if reclaim has scanned 100% !page_evictable pages, should_continue_reclaim() can return true and we keep on scanning? That sounds like it's both good and bad :( Is this actually a problem? What sort of behaviour could it cause and under what circumstances? Johannes's patch is an obvious bugfix and I'll run with it for now, but please let's have a further think abut the impact of the !page_evictable pages. -- 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 internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>