linux-kernel - Re: [PATCH v3] mm/hugetlb: add mempolicy check in the reservation routine

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Date:   Mon, 27 Jul 2020 17:19:53 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     mike.kravetz@...cle.com, mhocko@...nel.org, rientjes@...gle.com,
        mgorman@...e.de, walken@...gle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Jianchao Guo <guojianchao@...edance.com>
Subject: Re: [PATCH v3] mm/hugetlb: add mempolicy check in the reservation
 routine

On Sat, 25 Jul 2020 16:07:49 +0800 Muchun Song <songmuchun@...edance.com> wrote:

> In the reservation routine, we only check whether the cpuset meets
> the memory allocation requirements. But we ignore the mempolicy of
> MPOL_BIND case. If someone mmap hugetlb succeeds, but the subsequent
> memory allocation may fail due to mempolicy restrictions and receives
> the SIGBUS signal. This can be reproduced by the follow steps.
> 
>  1) Compile the test case.
>     cd tools/testing/selftests/vm/
>     gcc map_hugetlb.c -o map_hugetlb
> 
>  2) Pre-allocate huge pages. Suppose there are 2 numa nodes in the
>     system. Each node will pre-allocate one huge page.
>     echo 2 > /proc/sys/vm/nr_hugepages
> 
>  3) Run test case(mmap 4MB). We receive the SIGBUS signal.
>     numactl --membind=0 ./map_hugetlb 4
> 
> With this patch applied, the mmap will fail in the step 3) and throw
> "mmap: Cannot allocate memory".

This doesn't compile with CONFIG_NUMA=n - ther eis no implementation of
get_task_policy().

I think it needs more than a simple build fix - can we please rework
the patch so that its impact (mainly code size) on non-NUMA machines is
minimized?