linux-kernel - Re: [PATCH v3] z3fold: use per-page read/write lock

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Message-Id: <20161109143304.538885b06a4b5d2289da1e52@linux-foundation.org>
Date:   Wed, 9 Nov 2016 14:33:04 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Vitaly Wool <vitalywool@...il.com>
Cc:     Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org,
        Dan Streetman <ddstreet@...e.org>,
        Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH v3] z3fold: use per-page read/write lock

On Wed, 9 Nov 2016 11:55:31 +0100 Vitaly Wool <vitalywool@...il.com> wrote:

> Subject: [PATCH v3] z3fold: use per-page read/write lock

I've rewritten the title to "mm/z3fold.c: use per-page spinlock"

(I prefer to have "mm" in the title to easily identify it as an MM
patch, and using "mm: z3fold: ..." seems odd when the actual pathname
conveys the same info.)

> 
> Most of z3fold operations are in-page, such as modifying z3fold
> page header or moving z3fold objects within a page. Taking
> per-pool spinlock to protect per-page objects is therefore
> suboptimal, and the idea of having a per-page spinlock (or rwlock)
> has been around for some time. However, adding one directly to the
> z3fold header makes the latter quite big on some systems so that
> it won't fit in a signle chunk.
> 
> This patch implements spinlock-based per-page locking mechanism
> which is lightweight enough to fit into the z3fold header.