linux-kernel - Re: [PATCH v2] xen/gntdev: Use mempolicy instead of VM

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Date:   Thu, 17 Nov 2016 11:01:15 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Olaf Hering <olaf@...fle.de>
Cc:     david.vrabel@...rix.com, jgross@...e.com,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] xen/gntdev: Use mempolicy instead of VM_IO flag to
 avoid NUMA balancing

On 11/17/2016 06:28 AM, Olaf Hering wrote:
> On Wed, Nov 16, Boris Ostrovsky wrote:
>
>> Unfortunately I haven't been able to trigger NUMA balancing
>> so while I tested this in general I am not sure I actually
>> exercised the code path.
> Thanks for the patch!
>
> Would be nice to actually test the code path which caused the initial
> addition of VM_IO. I think I lack the hardware to excersise them.

To trip the original bug is even more difficult than to trigger NUMA
balancing. It was very sensitive to memory allocation.

>
>
> In my 4.4 based sources I get the following unresolved symbols. If that
> happens to work in mainline the failures should at least be considered
> during backporting of this proposed patch to the stable trees.
>
> ERROR: "__mpol_dup" [drivers/xen/xen-gntdev.ko] undefined!
> ERROR: "get_task_policy" [drivers/xen/xen-gntdev.ko] undefined!
>
> Appearently these symbols lack just an EXPORT_SYMBOL_GPL.


I just built 4.4.11 with this patch applied and haven't had any problems.

-boris



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