linux-kernel - Re: [PATCH] xen/gntdev: Grant maps should not be subject to NUMA balancing

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Message-ID: <56424B77.70106@oracle.com>
Date:	Tue, 10 Nov 2015 14:54:31 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	david.vrabel@...rix.com, xen-devel@...ts.xen.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen/gntdev: Grant maps should not be subject to NUMA
 balancing

On 11/10/2015 02:36 PM, Konrad Rzeszutek Wilk wrote:
> On Tue, Nov 10, 2015 at 02:22:44PM -0500, Boris Ostrovsky wrote:
>> Doing so will cause the grant to be unmapped and then, during
>> fault handling, the fault to be mistakenly treated as NUMA hint
>> fault.
>>
>> In addition, even if we those maps could partcipate in NUMA
>> balancing it wouldn't provide any benefit since we wouldn't be
>> able to determine physical page's node (even if/when VNUMA is
>> implemented).
>>
>> Marking grant maps' VMAs as VM_IO will exclude them from being
>> part of NUMA balancing.
>>
> Should this be 'cc:stable@...r.kernel.org' ?

This bug becomes a real problem with 4.4, now that NUMA balancing is on 
by default.

But we should probably include it in stable too. I'll resubmit it then 
with CC tag.

-boris

>
>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>> ---
>>   drivers/xen/gntdev.c |    2 +-
>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
>> index 67b9163..bf312df 100644
>> --- a/drivers/xen/gntdev.c
>> +++ b/drivers/xen/gntdev.c
>> @@ -802,7 +802,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>>   
>>   	vma->vm_ops = &gntdev_vmops;
>>   
>> -	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
>> +	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
>>   
>>   	if (use_ptemod)
>>   		vma->vm_flags |= VM_DONTCOPY;
>> -- 
>> 1.7.1
>>

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