Re: [PATCH] mm,page_alloc,cma: conditionally prefer cma pageblocks for movable allocations

From: Roman Gushchin <guro@fb.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Rik van Riel <riel@surriel.com>,
	Andrew Morton <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
	<linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
	Qian Cai <cai@lca.pw>, Mel Gorman <mgorman@techsingularity.net>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH] mm,page_alloc,cma: conditionally prefer cma pageblocks for movable allocations
Date: Wed, 11 Mar 2020 10:35:26 -0700	[thread overview]
Message-ID: <20200311173526.GH96999@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <8e67d88f-3ec8-4795-35dc-47e3735e530e@suse.cz>

On Wed, Mar 11, 2020 at 09:51:07AM +0100, Vlastimil Babka wrote:
> On 3/6/20 9:01 PM, Rik van Riel wrote:
> > Posting this one for Roman so I can deal with any upstream feedback and
> > create a v2 if needed, while scratching my head over the next piece of
> > this puzzle :)
> > 
> > ---8<---
> > 
> > From: Roman Gushchin <guro@fb.com>
> > 
> > Currently a cma area is barely used by the page allocator because
> > it's used only as a fallback from movable, however kswapd tries
> > hard to make sure that the fallback path isn't used.
> 
> Few years ago Joonsoo wanted to fix these kinds of weird MIGRATE_CMA corner
> cases by using ZONE_MOVABLE instead [1]. Unfortunately it was reverted due to
> unresolved bugs. Perhaps the idea could be resurrected now?

Hi Vlastimil!

Thank you for this reminder! I actually looked at it and also asked Joonsoo in private
about the state of this patch(set). As I understand, Joonsoo plans to resubmit
it later this year.

What Rik and I are suggesting seems to be much simpler, however it's perfectly
possible that Joonsoo's solution is preferable long-term.

So if the proposed patch looks ok for now, I'd suggest to go with it and return
to this question once we'll have a new version of ZONE_MOVABLE solution.

Thanks!