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Re: [PATCH 1/2] sched/wait: Break up long wake list walk

From ebiederm@xmission.com (Eric W. Biederman)
Newsgroups linux.kernel
Subject Re: [PATCH 1/2] sched/wait: Break up long wake list walk
Date 2017-08-17 01:30 +0200
Message-ID <uffV7-52i-3@gated-at.bofh.it> (permalink)
References (5 earlier) <ueAIi-4oo-5@gated-at.bofh.it> <ueSOR-7jm-7@gated-at.bofh.it> <ueSYx-7mo-15@gated-at.bofh.it> <ueSYx-7mo-13@gated-at.bofh.it> <ueTUB-7Wz-1@gated-at.bofh.it>
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Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Tue, Aug 15, 2017 at 3:57 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> Oh, and the page wait-queue really needs that key argument too, which
>> is another thing that swait queue code got rid of in the name of
>> simplicity.
>
> Actually, it gets worse.
>
> Because the page wait queues are hashed, it's not an all-or-nothing
> thing even for the non-exclusive cases, and it's not a "wake up first
> entry" for the exclusive case. Both have to be conditional on the wait
> entry actually matching the page and bit in question.
>
> So no way to use swait, or any of the lockless queuing code in general
> (so we can't do some clever private wait-list using llist.h either).
>
> End result: it looks like you fairly fundamentally do need to use a
> lock over the whole list traversal (like the standard wait-queues),
> and then add a cursor entry like Tim's patch if dropping the lock in
> the middle.
>
> Anyway, looking at the old code, we *used* to limit the page wait hash
> table to 4k entries, and we used to have one hash table per memory
> zone.
>
> The per-zone thing didn't work at all for the generic bit-waitqueues,
> because of how people used them on virtual addresses on the stack.
>
> But it *could* work for the page waitqueues, which are now a totally
> separate entity, and is obviously always physically addressed (since
> the indexing is by "struct page" pointer), and doesn't have that
> issue.
>
> So I guess we could re-introduce the notion of per-zone page waitqueue
> hash tables. It was disgusting to allocate and free though (and hooked
> into the memory hotplug code).
>
> So I'd still hope that we can instead just have one larger hash table,
> and that is sufficient for the problem.

If increasing the hash table size fixes the problem I am wondering if
rhash tables might be the proper solution to this problem.  They start
out small and then grow as needed.

Eric

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Thread

[PATCH 1/2] sched/wait: Break up long wake list walk Tim Chen <tim.c.chen@linux.intel.com> - 2017-08-15 03:20 +0200
  Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-15 03:50 +0200
    Re: [PATCH 1/2] sched/wait: Break up long wake list walk Andi Kleen <ak@linux.intel.com> - 2017-08-15 04:30 +0200
      Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-15 05:00 +0200
        Re: [PATCH 1/2] sched/wait: Break up long wake list walk Andi Kleen <ak@linux.intel.com> - 2017-08-15 05:20 +0200
          Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-15 05:30 +0200
            Re: [PATCH 1/2] sched/wait: Break up long wake list walk Tim Chen <tim.c.chen@linux.intel.com> - 2017-08-15 21:10 +0200
              Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-15 21:50 +0200
              Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-15 21:50 +0200
            Re: [PATCH 1/2] sched/wait: Break up long wake list walk Davidlohr Bueso <dave@stgolabs.net> - 2017-08-16 00:50 +0200
              Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-16 01:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-16 02:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk ebiederm@xmission.com (Eric W. Biederman) - 2017-08-17 01:30 +0200
              Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-16 01:00 +0200
    RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-17 18:20 +0200
      Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-17 18:30 +0200
        RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-17 22:20 +0200
          Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-17 22:50 +0200
            Re: [PATCH 1/2] sched/wait: Break up long wake list walk Mel Gorman <mgorman@techsingularity.net> - 2017-08-18 14:30 +0200
              RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-18 16:30 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Mel Gorman <mgorman@techsingularity.net> - 2017-08-18 16:50 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Tim Chen <tim.c.chen@linux.intel.com> - 2017-08-18 18:40 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Andi Kleen <ak@linux.intel.com> - 2017-08-18 18:50 +0200
                RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-18 19:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-18 19:50 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Mel Gorman <mgorman@techsingularity.net> - 2017-08-18 21:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-18 21:20 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Andi Kleen <ak@linux.intel.com> - 2017-08-18 22:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-18 22:20 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Mel Gorman <mgorman@techsingularity.net> - 2017-08-21 20:40 +0200
                RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-21 21:00 +0200
                RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-22 19:30 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-22 20:20 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-22 20:30 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Peter Zijlstra <peterz@infradead.org> - 2017-08-22 21:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-22 21:20 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Peter Zijlstra <peterz@infradead.org> - 2017-08-22 21:10 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Andi Kleen <ak@linux.intel.com> - 2017-08-22 21:40 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Christopher Lameter <cl@linux.com> - 2017-08-22 23:10 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Andi Kleen <ak@linux.intel.com> - 2017-08-22 23:30 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-23 01:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-23 01:20 +0200
                RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-23 17:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-22 21:40 +0200
                RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-22 22:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-22 22:50 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-22 23:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Peter Zijlstra <peterz@infradead.org> - 2017-08-22 23:00 +0200
                RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-23 16:50 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Tim Chen <tim.c.chen@linux.intel.com> - 2017-08-23 18:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-23 20:20 +0200
                RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-23 23:00 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 01:40 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Tim Chen <tim.c.chen@linux.intel.com> - 2017-08-24 19:50 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 20:20 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Mel Gorman <mgorman@techsingularity.net> - 2017-08-24 22:50 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Mel Gorman <mgorman@techsingularity.net> - 2017-08-23 18:10 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Andi Kleen <ak@linux.intel.com> - 2017-08-18 22:10 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-18 22:40 +0200
                RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-18 22:30 +0200
                Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-18 22:40 +0200
              Re: [PATCH 1/2] sched/wait: Break up long wake list walk Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-18 19:00 +0200
            RE: [PATCH 1/2] sched/wait: Break up long wake list walk "Liang, Kan" <kan.liang@intel.com> - 2017-08-18 15:10 +0200

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