linux-kernel - Re: [v2 PATCH 2/2] mm: swap: use smp_mb__after

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Message-ID: <CALvZod4pn1XJN7EVV9w6t2cYkHWG++GB6pJdBzBJO+w4k8aEEw@mail.gmail.com>
Date:   Mon, 16 Mar 2020 16:47:15 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [v2 PATCH 2/2] mm: swap: use smp_mb__after_atomic() to order LRU
 bit set

On Mon, Mar 16, 2020 at 3:24 PM Yang Shi <yang.shi@...ux.alibaba.com> wrote:
>
> Memory barrier is needed after setting LRU bit, but smp_mb() is too
> strong.  Some architectures, i.e. x86, imply memory barrier with atomic
> operations, so replacing it with smp_mb__after_atomic() sounds better,
> which is nop on strong ordered machines, and full memory barriers on
> others.  With this change the vm-calability cases would perform better
> on x86, I saw total 6% improvement with this patch and previous inline
> fix.
>
> The test data (lru-file-readtwice throughput) against v5.6-rc4:
>         mainline        w/ inline fix   w/ both (adding this)
>         150MB           154MB           159MB
>
> Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs")
> Cc: Shakeel Butt <shakeelb@...gle.com>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>

Reviewed-and-Tested-by: Shakeel Butt <shakeelb@...gle.com>