Messages in this thread Patch in this message | | | Date | Wed, 9 Feb 2011 19:28:46 +0100 | From | Andrea Arcangeli <> | Subject | Re: [patch] vmscan: fix zone shrinking exit when scan work is done |
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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@redhat.com>
nr_scanned is incremented even for !page_evictable... so it's not really useful to insist, just because we scanned something.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> ---
diff --git a/mm/vmscan.c b/mm/vmscan.c index 148c6e6..9741884 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1831,7 +1831,6 @@ out: */ static inline bool should_continue_reclaim(struct zone *zone, unsigned long nr_reclaimed, - unsigned long nr_scanned, struct scan_control *sc) { unsigned long pages_for_compaction; @@ -1841,15 +1840,8 @@ static inline bool should_continue_reclaim(struct zone *zone, if (!(sc->reclaim_mode & RECLAIM_MODE_COMPACTION)) return false; - /* - * If we failed to reclaim and have scanned the full list, stop. - * NOTE: Checking just nr_reclaimed would exit reclaim/compaction far - * faster but obviously would be less likely to succeed - * allocation. If this is desirable, use GFP_REPEAT to decide - * if both reclaimed and scanned should be checked or just - * reclaimed - */ - if (!nr_reclaimed && !nr_scanned) + /* If we failed to reclaim stop. */ + if (!nr_reclaimed) return false; /* @@ -1884,7 +1876,6 @@ static void shrink_zone(int priority, struct zone *zone, enum lru_list l; unsigned long nr_reclaimed; unsigned long nr_to_reclaim = sc->nr_to_reclaim; - unsigned long nr_scanned = sc->nr_scanned; restart: nr_reclaimed = 0; @@ -1923,8 +1914,7 @@ restart: shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0); /* reclaim/compaction might need reclaim to continue */ - if (should_continue_reclaim(zone, nr_reclaimed, - sc->nr_scanned - nr_scanned, sc)) + if (should_continue_reclaim(zone, nr_reclaimed, sc)) goto restart; throttle_vm_writeout(sc->gfp_mask);
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