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

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Date:   Fri, 7 Oct 2016 11:21:08 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
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 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.
-- 
Michal Hocko
SUSE Labs