linux-kernel - Re: [PATCH] mm/compaction: count pages and stop correctly during page isolation.

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Date:   Thu, 29 Oct 2020 21:20:16 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     Yang Shi <shy828301@...il.com>, Linux MM <linux-mm@...ck.org>,
        Rik van Riel <riel@...riel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>
Subject: Re: [PATCH] mm/compaction: count pages and stop correctly during page
 isolation.

On 29 Oct 2020, at 20:28, Andrew Morton wrote:

> On Thu, 29 Oct 2020 17:31:28 -0400 Zi Yan <ziy@...dia.com> wrote:
>
>>>
>>> Shall you add Fixes tag to commit
>>> 1da2f328fa643bd72197dfed0c655148af31e4eb? And may cc stable.
>>
>> Sure.
>>
>> Fixes: 1da2f328fa64 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”)
>>
>> 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 reservation finish.

—
Best Regards,
Yan Zi

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