linux-kernel - Re: [v4 PATCH 2/2] mm: mempolicy: handle vma with unmovable pages mapped correctly in mbind

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Message-ID: <6aeca7cf-d9da-95cc-e6dc-a10c2978c523@suse.cz>
Date:   Wed, 24 Jul 2019 10:19:34 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Yang Shi <yang.shi@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     mhocko@...nel.org, mgorman@...hsingularity.net, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [v4 PATCH 2/2] mm: mempolicy: handle vma with unmovable pages
 mapped correctly in mbind

On 7/23/19 7:35 AM, Yang Shi wrote:
> 
> 
> On 7/22/19 6:02 PM, Andrew Morton wrote:
>> On Mon, 22 Jul 2019 09:25:09 +0200 Vlastimil Babka <vbabka@...e.cz> wrote:
>>
>>>> since there may be pages off LRU temporarily.  We should migrate other
>>>> pages if MPOL_MF_MOVE* is specified.  Set has_unmovable flag if some
>>>> paged could not be not moved, then return -EIO for mbind() eventually.
>>>>
>>>> With this change the above test would return -EIO as expected.
>>>>
>>>> Cc: Vlastimil Babka <vbabka@...e.cz>
>>>> Cc: Michal Hocko <mhocko@...e.com>
>>>> Cc: Mel Gorman <mgorman@...hsingularity.net>
>>>> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
>>> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
>> Thanks.
>>
>> I'm a bit surprised that this doesn't have a cc:stable.  Did we
>> consider that?
> 
> The VM_BUG just happens on 4.9, and it is enabled only by CONFIG_VM. For 
> post-4.9 kernel, this fixes the semantics of mbind which should be not a 
> regression IMHO.

4.9 is a LTS kernel, so perhaps worth trying?

>>
>> Also, is this patch dependent upon "mm: mempolicy: make the behavior
>> consistent when MPOL_MF_MOVE* and MPOL_MF_STRICT were specified"?
>> Doesn't look that way..
> 
> No, it depends on patch #1.
> 
>>
>> Also, I have a note that you had concerns with "mm: mempolicy: make the
>> behavior consistent when MPOL_MF_MOVE* and MPOL_MF_STRICT were
>> specified".  What is the status now?
> 
> Vlastimil had given his Reviewed-by.

Yes, the concerns were resolved.