linux-kernel - Re: [RFC PATCH] mm, compaction: allow compaction for GFP

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Date:   Mon, 10 Oct 2016 08:44:33 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Mel Gorman <mgorman@...e.de>, Joonsoo Kim <js1304@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] mm, compaction: allow compaction for GFP_NOFS
 requests

On 10/07/2016 11:21 AM, Michal Hocko wrote:
> On Fri 07-10-16 10:15:07, Vlastimil Babka wrote:
>> On 10/07/2016 08:50 AM, Michal Hocko wrote:
>>> On Fri 07-10-16 07:27:37, Vlastimil Babka wrote:
> [...]
>>>> But make sure you don't break kcompactd and manual compaction from /proc, as
>>>> they don't currently set cc->gfp_mask. Looks like until now it was only used
>>>> to determine direct compactor's migratetype which is irrelevant in those
>>>> contexts.
>>>
>>> OK, I see. This is really subtle. One way to go would be to provide a
>>> fake gfp_mask for them. How does the following look to you?
>>
>> Looks OK. I'll have to think about the kcompactd case, as gfp mask implying
>> unmovable migratetype might restrict it without good reason. But that would
>> be separate patch anyway, yours doesn't change that (empty gfp_mask also
>> means unmovable migratetype) and that's good.
>
> OK, I see. A follow up patch would be really trivial AFAICS. Just add
> __GFP_MOVABLE to the mask. But I am not familiar with all these details
> enough to propose a patch with full description.

Hm, actually the migratetype only matters for async compaction, and 
kcompactd uses sync_light, so __GFP_MOVABLE will have no effect right now.