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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 2 Nov 2016 09:18:37 -0600
Message-ID: <CA+55aFxhxfevU1uKwHmPheoU7co4zxxcri+AiTpKz=1_Nd0_ig@mail.gmail.com>
Subject: Re: [PATCH 2/2] mm: add PageWaiters bit to indicate waitqueue should
 be checked
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Sender: owner-linux-mm@kvack.org
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To: Nicholas Piggin <npiggin@gmail.com>
Cc: linux-mm <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>, Mel Gorman <mgorman@techsingularity.net>, Peter Zijlstra <peterz@infradead.org>, Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>

On Wed, Nov 2, 2016 at 1:03 AM, Nicholas Piggin <npiggin@gmail.com> wrote:
> +       __wake_up_locked_key(q, TASK_NORMAL, &key);
> +       if (!waitqueue_active(q) || !key.page_match) {
> +               ClearPageWaiters(page);

Is that "page_match" optimization really worth it? I'd rather see
numbers for that particular optimization. I'd rather see the
contention bit being explicitly not precise.

Also, it would be lovely to get numbers against the plain 4.8
situation with the per-zone waitqueues. Maybe that used to help your
workload, so the 2.2% improvement might be partly due to me breaking
performance on your machine.

But other than that this all looks fine to me.

                   Linus

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