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Re: [PATCH 1/5] mm, vmscan: Do not account skipped pages as scanned

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On Mon, Jul 25, 2016 at 05:04:56PM +0900, Minchan Kim wrote:
> > @@ -1429,6 +1429,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> >  			continue;
> >  		}
> >  
> > +		/* Pages skipped do not contribute to scan */
> > +		scan++;
> > +
> 
> As I mentioned in previous version, under irq-disabled-spin-lock, such
> unbounded operation would make the latency spike worse if there are
> lot of pages we should skip.
> 
> Don't we take care it?

It's not unbounded, it's bound by the size of the LRU list and it's not
going to be enough to trigger a warning. While the lock hold time may be
undesirable, unlocking it every SWAP_CLUSTER_MAX pages may increase overall
contention. There also is the question of whether skipped pages should be
temporarily putback before unlocking the LRU to avoid isolated pages being
unavailable for too long. It also cannot easily just return early without
prematurely triggering OOM due to a lack of progress. I didn't feel the
complexity was justified.

-- 
Mel Gorman
SUSE Labs

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[PATCH 0/5] Candidate fixes for premature OOM kills with node-lru v1 Mel Gorman <mgorman@techsingularity.net> - 2016-07-20 17:30 +0200
  [PATCH 2/5] mm: add per-zone lru list stat Mel Gorman <mgorman@techsingularity.net> - 2016-07-20 17:30 +0200
    Re: [PATCH 2/5] mm: add per-zone lru list stat Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-07-21 09:10 +0200
      Re: [PATCH 2/5] mm: add per-zone lru list stat Fengguang Wu <fengguang.wu@intel.com> - 2016-07-23 02:50 +0200
        Re: [PATCH 2/5] mm: add per-zone lru list stat Minchan Kim <minchan@kernel.org> - 2016-07-23 03:30 +0200
  [PATCH 3/5] mm, vmscan: Remove highmem_file_pages Mel Gorman <mgorman@techsingularity.net> - 2016-07-20 17:30 +0200
  [PATCH 1/5] mm, vmscan: Do not account skipped pages as scanned Mel Gorman <mgorman@techsingularity.net> - 2016-07-20 17:30 +0200
    Re: [PATCH 1/5] mm, vmscan: Do not account skipped pages as scanned Minchan Kim <minchan@kernel.org> - 2016-07-21 07:20 +0200
      Re: [PATCH 1/5] mm, vmscan: Do not account skipped pages as scanned Mel Gorman <mgorman@techsingularity.net> - 2016-07-21 10:20 +0200
        Re: [PATCH 1/5] mm, vmscan: Do not account skipped pages as scanned Minchan Kim <minchan@kernel.org> - 2016-07-21 10:40 +0200
    Re: [PATCH 1/5] mm, vmscan: Do not account skipped pages as scanned Minchan Kim <minchan@kernel.org> - 2016-07-25 10:10 +0200
      Re: [PATCH 1/5] mm, vmscan: Do not account skipped pages as scanned Mel Gorman <mgorman@techsingularity.net> - 2016-07-25 11:30 +0200
  [PATCH 4/5] mm: Remove reclaim and compaction retry approximations Mel Gorman <mgorman@techsingularity.net> - 2016-07-20 17:30 +0200
  Re: [PATCH 0/5] Candidate fixes for premature OOM kills with  node-lru v1 Minchan Kim <minchan@kernel.org> - 2016-07-21 09:10 +0200
    Re: [PATCH 0/5] Candidate fixes for premature OOM kills with  node-lru v1 Mel Gorman <mgorman@techsingularity.net> - 2016-07-21 11:20 +0200
  Re: [PATCH 0/5] Candidate fixes for premature OOM kills with  node-lru v1 Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-07-21 09:30 +0200
    Re: [PATCH 0/5] Candidate fixes for premature OOM kills with  node-lru v1 Minchan Kim <minchan@kernel.org> - 2016-07-21 10:40 +0200
    Re: [PATCH 0/5] Candidate fixes for premature OOM kills with  node-lru v1 Mel Gorman <mgorman@techsingularity.net> - 2016-07-21 11:20 +0200

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