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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 4 Nov 2016 08:59:15 -0700
Message-ID: <CA+55aFxoT82RocOCZ9+k7_NZ+KZNtCQrwzNd=reB0n03xDj4-A@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 Fri, Nov 4, 2016 at 12:29 AM, Nicholas Piggin <npiggin@gmail.com> wrote:
> Oh, okay, the zone lookup. Well I am of the impression that most of the
> cache misses are coming from the waitqueue hash table itself.

No.

Nick, stop this idiocy.

NUMBERS, Nick. NUMBERS.

I posted numbers in "page_waitqueue() considered harmful" on linux-mm.

And quite frankly, before _you_ start posting numbers, that zone crap
IS NEVER COMING BACK.

What's so hard about this concept? We don't add crazy complexity
without numbers. Numbers that I bet you will not be able to provide,
because quiet frankly, even in your handwavy "what about lots of
concurrent IO from hundreds of threads" situation, that wait-queue
will NOT BE NOTICEABLE.

So no "impressions". No "what abouts". No "threaded IO" excuses. The
_only_ thing that matters is numbers. If you don't have them, don't
bother talking about that zone patch.

             Linus

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