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Re: [RFC 3/4] mm, page_alloc: move cpuset seqcount checking to slowpath

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On Tue, Jan 17, 2017 at 11:16:09PM +0100, Vlastimil Babka wrote:
> This is a preparation for the following patch to make review simpler. While
> the primary motivation is a bug fix, this could also save some cycles in the
> fast path.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

To be clear, the fast path savings will be when cpusets are active even
though that is still a good thing.  Most of the time, they are disabled
static branches. I see there were concerns raised that this would retry
the kswapd paths but I don't really see the issue. The same wakeup could
occur due to a cpuset switch with the existing retry. Even a potentially
spurious wakeup of kswapd is ok if the slow paths were being hit anyway
as kswapd is probably still awake from the first wakeup. If anything,
the fact that kswapd wakeups ignore cpusets and potentially wakes kswapd
on forbidden nodes is more problematic but not worth fixing. If kswapd
needs to wake on a node outside the cpuset then it's going to be by some
active process outside the cpuset some time in the future so;

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs

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[RFC 0/4] fix premature OOM due to cpuset races Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 01:10 +0100
  [RFC 4/4] mm, page_alloc: fix premature OOM when racing with cpuset mems update Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 01:10 +0100
    Re: [RFC 4/4] mm, page_alloc: fix premature OOM when racing with cpuset mems update "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2017-01-18 08:20 +0100
      Re: [RFC 4/4] mm, page_alloc: fix premature OOM when racing with  cpuset mems update Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 10:40 +0100
    Re: [RFC 4/4] mm, page_alloc: fix premature OOM when racing with  cpuset mems update Mel Gorman <mgorman@techsingularity.net> - 2017-01-18 11:20 +0100
  [RFC 3/4] mm, page_alloc: move cpuset seqcount checking to slowpath Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 01:20 +0100
    Re: [RFC 3/4] mm, page_alloc: move cpuset seqcount checking to slowpath "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2017-01-18 08:40 +0100
      Re: [RFC 3/4] mm, page_alloc: move cpuset seqcount checking to  slowpath Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 10:30 +0100
    Re: [RFC 3/4] mm, page_alloc: move cpuset seqcount checking to  slowpath Mel Gorman <mgorman@techsingularity.net> - 2017-01-18 11:10 +0100
    Re: [RFC 3/4] mm, page_alloc: move cpuset seqcount checking to  slowpath Michal Hocko <mhocko@kernel.org> - 2017-01-18 11:10 +0100
      Re: [RFC 3/4] mm, page_alloc: move cpuset seqcount checking to  slowpath Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 11:10 +0100
        Re: [RFC 3/4] mm, page_alloc: move cpuset seqcount checking to  slowpath Michal Hocko <mhocko@kernel.org> - 2017-01-18 11:20 +0100
  [RFC 2/4] mm, page_alloc: fix fast-path race with cpuset update or removal Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 01:20 +0100
    Re: [RFC 2/4] mm, page_alloc: fix fast-path race with cpuset update  or removal Michal Hocko <mhocko@kernel.org> - 2017-01-18 10:40 +0100
    Re: [RFC 2/4] mm, page_alloc: fix fast-path race with cpuset update  or removal Mel Gorman <mgorman@techsingularity.net> - 2017-01-18 10:50 +0100
  Re: [RFC 0/4] fix premature OOM due to cpuset races Michal Hocko <mhocko@kernel.org> - 2017-01-18 10:40 +0100
  [RFC 5/4] mm, page_alloc: fix premature OOM due to vma mempolicy  update Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 17:30 +0100
    Re: [RFC 5/4] mm, page_alloc: fix premature OOM due to vma mempolicy  update Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 17:30 +0100

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