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

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Message-ID: <0c993a89-83a1-d8a8-4927-d36660179256@oracle.com>
Date:   Thu, 10 Nov 2016 11:39:06 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Olaf Hering <olaf@...fle.de>
Cc:     konrad.wilk@...cle.com, david.vrabel@...rix.com,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        xen-devel@...ts.xen.org
Subject: Re: [Xen-devel] [PATCH RESEND] xen/gntdev: Grant maps should not be
 subject to NUMA balancing

On 11/10/2016 11:26 AM, Olaf Hering wrote:
> On Tue, Nov 10, Boris Ostrovsky wrote:

Perfect timing. This is from Nov. 10 2015.

>
>> 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 those maps could partcipate in NUMA
>> balancing, it wouldn't provide any benefit since we are unable
>> 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.
> This breaks qdisk+aio because now such pages are rejected with -EFAULT:

Is this something new? Because this patch has been there for a year.

-boris

>
> check_vma_flags
> __get_user_pages
> __get_user_pages_locked
> __get_user_pages_unlocked
> get_user_pages_fast
> iov_iter_get_pages
> dio_refill_pages
> do_direct_IO
> do_blockdev_direct_IO
> do_blockdev_direct_IO
> ext4_direct_IO_read
> generic_file_read_iter
> aio_run_iocb
>
> domU.cfg:
> builder=hvm
> disk=['vdev=xvda, direct-io-safe, backendtype=qdisk, target=img.raw']
>
>> @@ -802,7 +802,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>> -	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
>> +	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
>
> Olaf




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