linux-kernel - Re: [PATCH v2] mm/page_alloc: call check_new_pages() while zone spinlock is not held

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Message-ID: <CANn89iKy2_hutqReS9oa+e9d6Eao639=-PXA=9r5oNkqeh46rg@mail.gmail.com>
Date:   Wed, 9 Mar 2022 09:32:29 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v2] mm/page_alloc: call check_new_pages() while zone
 spinlock is not held

On Wed, Mar 9, 2022 at 4:32 AM Mel Gorman <mgorman@...hsingularity.net> wrote:

> We should because it was an oversight. Thanks for pointing that out.
>
> > Or was it a conscious choice of yours ?
> > (I presume part of the performance gains came from
> > not having to bring ~7 cache lines per 32KB chunk on x86)
> >
>
> There will be a performance penalty due to the check but it's a correctness
> vs performance issue.
>
> This? It's boot tested only.
>
> --8<--
> mm/page_alloc: check high-order pages for corruption during PCP operations
>
> Eric Dumazet pointed out that commit 44042b449872 ("mm/page_alloc: allow
> high-order pages to be stored on the per-cpu lists") only checks the head
> page during PCP refill and allocation operations. This was an oversight
> and all pages should be checked. This will incur a small performance
> penalty but it's necessary for correctness.
>
> Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
> Reported-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> ---

SGTM, thanks Mel !

Acked-by: Eric Dumazet <edumazet@...gle.com>