[PATCH] mm: disable numa migration faults for dax vmas

[PATCH] mm: disable numa migration faults for dax vmas

[Dan Williams]

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.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/mempolicy.h |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index 5e5b2969d931..d72c691afaa6 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -7,6 +7,7 @@
 
 
 #include <linux/mmzone.h>
+#include <linux/dax.h>
 #include <linux/slab.h>
 #include <linux/rbtree.h>
 #include <linux/spinlock.h>
@@ -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;

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Re: [PATCH] mm: disable numa migration faults for dax vmas

[Andrew Morton]

On Fri, 11 Nov 2016 20:21:41 -0800 Dan Williams <dan.j.williams@intel.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;
 
_

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Re: [PATCH] mm: disable numa migration faults for dax vmas

[Dan Williams]

On Mon, Nov 14, 2016 at 4:25 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Fri, 11 Nov 2016 20:21:41 -0800 Dan Williams <dan.j.williams@intel.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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