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SubjectRe: [External] Re: [PATCH v3] mm/hugetlb: add mempolicy check in the reservation routine
On Tue, Jul 28, 2020 at 8:19 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Sat, 25 Jul 2020 16:07:49 +0800 Muchun Song <songmuchun@bytedance.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?
>

OK. I will do that, thanks.


--
Yours,
Muchun

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