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Date:   Mon, 14 Nov 2016 17:06:23 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...e.com>,
        linux-nvdimm <linux-nvdimm@...1.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH] mm: disable numa migration faults for dax vmas

On Mon, Nov 14, 2016 at 4:25 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Fri, 11 Nov 2016 20:21:41 -0800 Dan Williams <dan.j.williams@...el.com> wrote:
>
>> Mark dax vmas as not migratable to exclude them from task_numa_work().
>> This is especially relevant for device-dax which wants to ensure
>> predictable access latency and not incur periodic faults.
>>
>> ...
>>
>> @@ -177,6 +178,9 @@ static inline bool vma_migratable(struct vm_area_struct *vma)
>>       if (vma->vm_flags & (VM_IO | VM_PFNMAP))
>>               return false;
>>
>> +     if (vma_is_dax(vma))
>> +             return false;
>> +
>>  #ifndef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
>>       if (vma->vm_flags & VM_HUGETLB)
>>               return false;
>
> I don't think the reader could figure out why this code is here, so...  this?
>
> --- a/include/linux/mempolicy.h~mm-disable-numa-migration-faults-for-dax-vmas-fix
> +++ a/include/linux/mempolicy.h
> @@ -180,6 +180,10 @@ static inline bool vma_migratable(struct
>         if (vma->vm_flags & (VM_IO | VM_PFNMAP))
>                 return false;
>
> +       /*
> +        * DAX device mappings require predictable access latency, so avoid
> +        * incurring periodic faults.
> +        */
>         if (vma_is_dax(vma))
>                 return false;
>

Yes, thanks for fixing it up.

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