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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