Re: [PATCH 5/5] mm, vmscan: Account for skipped pages as a partial scan

From	Mel Gorman <mgorman@techsingularity.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH 5/5] mm, vmscan: Account for skipped pages as a partial scan
Date	2016-07-25 12:00 +0200
Message-ID	<rYKQ2-2ZK-13@gated-at.bofh.it> (permalink)
References	<rXmZs-8w7-5@gated-at.bofh.it> <rXmZs-8w7-9@gated-at.bofh.it> <rYJAB-2kh-9@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, Jul 25, 2016 at 05:39:13PM +0900, Minchan Kim wrote:
> > @@ -1465,14 +1471,24 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> >  	 */
> >  	if (!list_empty(&pages_skipped)) {
> >  		int zid;
> > +		unsigned long total_skipped = 0;
> >  
> > -		list_splice(&pages_skipped, src);
> >  		for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> >  			if (!nr_skipped[zid])
> >  				continue;
> >  
> >  			__count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
> > +			total_skipped += nr_skipped[zid];
> >  		}
> > +
> > +		/*
> > +		 * Account skipped pages as a partial scan as the pgdat may be
> > +		 * close to unreclaimable. If the LRU list is empty, account
> > +		 * skipped pages as a full scan.
> > +		 */
> 
> node-lru made OOM detection lengthy because a freeing of any zone will
> reset NR_PAGES_SCANNED easily so that it's hard to meet a situation
> pgdat_reclaimable returns *false*.
> 

Your patch should go a long way to addressing that as it checks the zone
counters first before conducting the scan. Remember as well that the longer
detection of OOM only applies to zone-constrained allocations and there
is always the possibility that highmem shrinking of pages frees lowmem
memory if buffers are used.

-- 
Mel Gorman
SUSE Labs

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[PATCH 5/5] mm, vmscan: Account for skipped pages as a partial scan Mel Gorman <mgorman@techsingularity.net> - 2016-07-21 16:20 +0200
  Re: [PATCH 5/5] mm, vmscan: Account for skipped pages as a partial  scan Johannes Weiner <hannes@cmpxchg.org> - 2016-07-22 18:10 +0200
  Re: [PATCH 5/5] mm, vmscan: Account for skipped pages as a partial  scan Minchan Kim <minchan@kernel.org> - 2016-07-25 10:40 +0200
    Re: [PATCH 5/5] mm, vmscan: Account for skipped pages as a partial  scan Mel Gorman <mgorman@techsingularity.net> - 2016-07-25 12:00 +0200

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