Re: [PATCH v3 00/16] Support non-lru page migration

From: Minchan Kim <minchan@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	jlayton@poochiereds.net, bfields@fieldses.org,
	Vlastimil Babka <vbabka@suse.cz>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	koct9i@gmail.com, aquini@redhat.com,
	virtualization@lists.linux-foundation.org,
	Mel Gorman <mgorman@suse.de>, Hugh Dickins <hughd@google.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Rik van Riel <riel@redhat.com>,
	rknize@motorola.com, Gioh Kim <gi-oh.kim@profitbricks.com>,
	Sangseok Lee <sangseok.lee@lge.com>,
	Chan Gyun Jeong <chan.jeong@lge.com>,
	Al Viro <viro@ZenIV.linux.org.uk>,
	YiPing Xu <xuyiping@hisilicon.com>
Subject: Re: [PATCH v3 00/16] Support non-lru page migration
Date: Mon, 11 Apr 2016 13:35:57 +0900	[thread overview]
Message-ID: <20160411043557.GC4804@bbox> (raw)
In-Reply-To: <20160404131718.GA18963@e106921-lin.trondheim.arm.com>

On Mon, Apr 04, 2016 at 03:17:18PM +0200, John Einar Reitan wrote:
> On Wed, Mar 30, 2016 at 04:11:59PM +0900, Minchan Kim wrote:
> > Recently, I got many reports about perfermance degradation
> > in embedded system(Android mobile phone, webOS TV and so on)
> > and failed to fork easily.
> > 
> > The problem was fragmentation caused by zram and GPU driver
> > pages. Their pages cannot be migrated so compaction cannot
> > work well, either so reclaimer ends up shrinking all of working
> > set pages. It made system very slow and even to fail to fork
> > easily.
> > 
> > Other pain point is that they cannot work with CMA.
> > Most of CMA memory space could be idle(ie, it could be used
> > for movable pages unless driver is using) but if driver(i.e.,
> > zram) cannot migrate his page, that memory space could be
> > wasted. In our product which has big CMA memory, it reclaims
> > zones too exccessively although there are lots of free space
> > in CMA so system was very slow easily.
> > 
> > To solve these problem, this patch try to add facility to
> > migrate non-lru pages via introducing new friend functions
> > of migratepage in address_space_operation and new page flags.
> > 
> > 	(isolate_page, putback_page)
> > 	(PG_movable, PG_isolated)
> > 
> > For details, please read description in
> > "mm/compaction: support non-lru movable page migration".
> 
> Thanks, this mirrors what we see with the ARM Mali GPU drivers too.
> 
> One thing with the current design which worries me is the potential
> for multiple calls due to many separated pages being migrated.
> On GPUs (or any other device) which has an IOMMU and L2 cache, which
> isn't coherent with the CPU, we must do L2 cache flush & invalidation
> per page. I guess batching pages isn't easily possible?
> 

Hmm, I think it seems to cause many code stirring but surely worth
to work. So, IMMO, it would be better to add such feature after soft
landing of current work.

Anyway, I will Cc'ed you in next revision.

Thanks.