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

[Mike Kravetz <mike.kravetz@oracle.com>]

On 7/25/20 1:07 AM, Muchun Song 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".
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Reported-by: Jianchao Guo <guojianchao@bytedance.com>
> Suggested-by: Michal Hocko <mhocko@kernel.org>

Thank you Muchun and Michal,

This patch forced me to once again look at the bad the interaction of
hugetlb reservations and cpusets or mempolicy.  This new code will help
produce a quick failure as described in the commit message, and it does
not make existing interactions any worse.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

-- 
Mike Kravetz