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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 21 Dec 2016 11:50:49 -0800
Message-ID: <CA+55aFwQtaKGDzNFsanMavTH=TBoHgjGqQbwqbLvbjs7Y0EWCw@mail.gmail.com>
Subject: Re: [RFC][PATCH] make global bitlock waitqueues per-node
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To: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Dave Hansen <dave.hansen@linux.intel.com>, Bob Peterson <rpeterso@redhat.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Steven Whitehouse <swhiteho@redhat.com>, Andrew Lutomirski <luto@kernel.org>, Andreas Gruenbacher <agruenba@redhat.com>, Mel Gorman <mgorman@techsingularity.net>, linux-mm <linux-mm@kvack.org>, Hugh Dickins <hughd@google.com>

On Wed, Dec 21, 2016 at 11:01 AM, Nicholas Piggin <npiggin@gmail.com> wrote:
> Peter's patch is less code and in that regard a bit nicer. I tried
> going that way once, but I just thought it was a bit too sloppy to
> do nicely with wait bit APIs.

So I have to admit that when I read through your and PeterZ's patches
back-to-back, yours was easier to understand.

PeterZ's is smaller but kind of subtle. The whole "return zero from
lock_page_wait() and go around again" and the locking around that
isn't exactly clear. In contrast, yours has the obvious waitqueue
spinlock.

I'll think about it.  And yes, it would be good to have more testing,
but at the same time xmas is imminent, and waiting around too much
isn't going to help either..

              Linus

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