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

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Date:   Tue, 15 Aug 2017 12:47:54 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...e.hu>, Kan Liang <kan.liang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched/wait: Break up long wake list walk

On Tue, Aug 15, 2017 at 12:41 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> So if we have unnecessarily collisions because we have waiters looking
> at different bits of the same page, we could just hash in the bit
> number that we're waiting for too.

Oh, nope, we can't do that, because we only have one "PageWaters" bit
per page, and it is shared across all bits we're waiting for on that
page.

So collisions between different bits on the same page are inevitable,
and we just need to make sure the hash table is big enough that we
don't get unnecessary collisions between different pages.

                Linus