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From:   Zi Yan <ziy@nvidia.com>
To:     Andrew Morton <akpm@linux-foundation.org>
CC:     Yang Shi <shy828301@gmail.com>, Linux MM <linux-mm@kvack.org>,
        Rik van Riel <riel@surriel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        <stable@vger.kernel.org>
Subject: Re: [PATCH] mm/compaction: count pages and stop correctly during page
 isolation.
Date:   Thu, 29 Oct 2020 21:20:16 -0400
Message-ID: <7DC14FB8-8DA4-4DB4-BB0B-3409CA8D6DD9@nvidia.com>
In-Reply-To: <20201029172822.da31fa5ab34c3a795361768f@linux-foundation.org>
References: <20201029200435.3386066-1-zi.yan@sent.com>
 <CAHbLzkpka7s1DFeXO5dxfGvxZFcTYb9KH0AE_AXuxeFO4q_rtg@mail.gmail.com>
 <EC915762-AE2E-4ACB-AB27-E7C95A584A0C@nvidia.com>
 <20201029172822.da31fa5ab34c3a795361768f@linux-foundation.org>
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On 29 Oct 2020, at 20:28, Andrew Morton wrote:

> On Thu, 29 Oct 2020 17:31:28 -0400 Zi Yan <ziy@nvidia.com> wrote:
>
>>>
>>> Shall you add Fixes tag to commit
>>> 1da2f328fa643bd72197dfed0c655148af31e4eb? And may cc stable.
>>
>> Sure.
>>
>> Fixes: 1da2f328fa64 (=E2=80=9Cmm,thp,compaction,cma: allow THP migrati=
on for CMA allocations=E2=80=9D)
>>
>> stable cc'ed.
>
> A think a cc:stable really requires a description of the end-user
> visible effects of the bug.  Could you please provide that?

Sure.

For example, in a system with 16GB memory and an 8GB CMA region reserved =
by hugetlb_cma,
if we first allocate 10GB THPs and mlock them (so some THPs are allocated=
 in the CMA
region and mlocked), reserving 6 1GB hugetlb pages via
/sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages will get stuck =
(looping
in too_many_isolated function) until we kill either task. With the patch =
applied,
oom will kill the application with 10GB THPs and let hugetlb page reserva=
tion finish.

=E2=80=94
Best Regards,
Yan Zi

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