linux-kernel - Re: [PATCH v4 1/3] mm: introduce compaction and migration for virtio ballooned pages

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Date:	Fri, 3 Aug 2012 09:26:57 -0300
From:	Rafael Aquini <aquini@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Rafael Aquini <aquini@...ux.com>
Subject: Re: [PATCH v4 1/3] mm: introduce compaction and migration for virtio
 ballooned pages

On Mon, Jul 23, 2012 at 11:33:32AM +0900, Minchan Kim wrote:
> Look at memory-hotplug, offline_page calls has_unmovable_pages, scan_lru_pages
> and do_migrate_range which calls isolate_lru_page. They consider only LRU pages
> to migratable ones.
>
As promised, I looked into those bits. Yes, they only isolate LRU pages, and as
such, having this series merged or not doesn't change a bit for that code path.
In fact, having this series merged and teaching hotplug's
offline_pages()/do_migrate_rage() about ballooned pages might be extremely
beneficial in the rare event offlining memory stumbles across a balloon page.

As Rik said, I believe this is something we can look into in the near future.
 
> IMHO, better approach is that after we can get complete free pageblocks
> by compaction or reclaim, move balloon pages into that pageblocks and make
> that blocks to unmovable. It can prevent fragmentation and it makes
> current or future code don't need to consider balloon page.
> 
I totally agree with Rik on this one, as well. This is the wrong approach here.

All that said, I'll soon respin a v5 based on your comments on branch hinting and
commentary improvements, as well as addressing AKPM's concerns. I'll also revert
isolate_balloon_page() last changes back to make it a public symbol again, as
(I believe) we'll shortly be using it for letting hotplug bits aware of how to
isolate ballooned pages.


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