linux-kernel - Re: [PATCH 3/7] mm: remove redundant smp

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Message-ID: <CAMZfGtWjunhRYQNW4u4Rea8N+csKPvzUmKfgUBnWBdJdagjs-g@mail.gmail.com>
Date:   Tue, 27 Jul 2021 21:39:17 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Qi Zheng <zhengqi.arch@...edance.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH 3/7] mm: remove redundant smp_wmb()

On Sun, Jul 18, 2021 at 12:31 PM Qi Zheng <zhengqi.arch@...edance.com> wrote:
>
> The smp_wmb() which is in the __pte_alloc() is used to
> ensure all ptes setup is visible before the pte is made
> visible to other CPUs by being put into page tables. We
> only need this when the pte is actually populated, so
> move it to pte_install(). __pte_alloc_kernel(),
> __p4d_alloc(), __pud_alloc() and __pmd_alloc() are similar
> to this case.
>
> We can also defer smp_wmb() to the place where the pmd entry
> is really populated by preallocated pte. There are two kinds
> of user of preallocated pte, one is filemap & finish_fault(),
> another is THP. The former does not need another smp_wmb()
> because the smp_wmb() has been done by pte_install().
> Fortunately, the latter also does not need another smp_wmb()
> because there is already a smp_wmb() before populating the
> new pte when the THP use preallocated pte to split huge pmd.

s/use/uses a/g
s/split huge/split a huge/g

>
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>

Reviewed-by: Muchun Song <songmuchun@...edance.com>