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

[Muchun Song]

On Tue, Jul 28, 2020 at 8:19 AM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Sat, 25 Jul 2020 16:07:49 +0800 Muchun Song <songmuchun@xxxxxxxxxxxxx> 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