linux-kernel - Re: [PATCH 2/3] z3fold: remove redundant locking

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Message-ID: <CAMJBoFNzsAf8463=H6Phg9vaPzXWVJ5qTQMMcB52O3ZQVVo=Ew@mail.gmail.com>
Date:   Sat, 22 Oct 2016 20:51:04 +0200
From:   Vitaly Wool <vitalywool@...il.com>
To:     Dan Streetman <ddstreet@...e.org>
Cc:     Linux-MM <linux-mm@...ck.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/3] z3fold: remove redundant locking

On Thu, Oct 20, 2016 at 10:15 PM, Dan Streetman <ddstreet@...e.org> wrote:
> On Wed, Oct 19, 2016 at 12:35 PM, Vitaly Wool <vitalywool@...il.com> wrote:
>> The per-pool z3fold spinlock should generally be taken only when
>> a non-atomic pool variable is modified. There's no need to take it
>> to map/unmap an object. This patch introduces per-page lock that
>> will be used instead to protect per-page variables in map/unmap
>> functions.
>
> I think the per-page lock must be held around almost all access to any
> page zhdr data; previously that was protected by the pool lock.

Right, except for list operations. At this point I think per-page
locks will have to be
thought over again, and there is some nice performance gain from making spinlock
a rwlock anyway, so I'll stick with the latest patchset, fixing tiny
bits like wrong
unbuddied_nr increment in the other patch.

Best regards,
   Vitaly