On 10/13/2016 05:19 AM, Jan Stancek wrote:
> Hi,
> 
> I'm running into ENOMEM failures with libhugetlbfs testsuite [1] on
> a power8 lpar system running 4.8 or latest git [2]. Repeated runs of
> this suite trigger multiple OOMs, that eventually kill entire system,
> it usually takes 3-5 runs:
> 
>  * Total System Memory......:  18024 MB
>  * Shared Mem Max Mapping...:    320 MB
>  * System Huge Page Size....:     16 MB
>  * Available Huge Pages.....:     20
>  * Total size of Huge Pages.:    320 MB
>  * Remaining System Memory..:  17704 MB
>  * Huge Page User Group.....:  hugepages (1001)
> 
> I see this only on ppc (BE/LE), x86_64 seems unaffected and successfully
> ran the tests for ~12 hours.
> 
> Bisect has identified following patch as culprit:
>   commit 67961f9db8c477026ea20ce05761bde6f8bf85b0
>   Author: Mike Kravetz <mike.krav...@oracle.com>
>   Date:   Wed Jun 8 15:33:42 2016 -0700
>     mm/hugetlb: fix huge page reserve accounting for private mappings
> 

Thanks Jan, I'll take a look.

> 
> Following patch (made with my limited insight) applied to
> latest git [2] fixes the problem for me:
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index ec49d9e..7261583 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1876,7 +1876,7 @@ static long __vma_reservation_common(struct hstate *h,
>                  * return value of this routine is the opposite of the
>                  * value returned from reserve map manipulation routines 
> above.
>                  */
> -               if (ret)
> +               if (ret >= 0)
>                         return 0;
>                 else
>                         return 1;
> 

Do note that this code is only executed if this condition is true:

        else if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) && ret >= 0) {

So, we would always return 0.  This always tells the calling code that a
reservation exists.

-- 
Mike Kravetz

> Regards,
> Jan
> 
> [1] https://github.com/libhugetlbfs/libhugetlbfs
> [2] v4.8-14230-gb67be92
> 

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