linux-kernel - Re: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that may be migrated

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Date:	Mon, 4 Dec 2006 14:34:35 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	clameter@....com, Andy Whitcroft <apw@...dowen.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that
 may be migrated

On Mon, 4 Dec 2006 20:34:29 +0000 (GMT)
Mel Gorman <mel@....ul.ie> wrote:

> > IOW: big-picture where-do-we-go-from-here stuff.
> >
> 
> Start with lumpy reclaim,

I had lumpy-reclaim in my todo-queue but it seems to have gone away.  I
think I need a lumpy-reclaim resend, please.

> then I'd like to merge page clustering piece by 
> piece, ideally with one of the people with e1000 problems testing to see 
> does it make a difference.
> 
> Assuming they are shown to help, where we'd go from there would be stuff 
> like;
> 
> 1. Keep non-movable and reapable allocations at the lower PFNs as much as
>     possible. This is so DIMMS for higher PFNs can be removed (doesn't
>     exist)

"as much as possible" won't suffice, I suspect.  If there's any chance at
all that a non-moveable page can land in a hot-unpluggable region then
there will be failure scenarios.  Easy-to-hit ones, I suspect.

> 2. Use page migration to compact memory rather than depending solely on
>     reclaim (doesn't exist)

Yup.

> 3. Introduce a mechanism for marking a group of pages as being offlined so
>     that they are not reallocated (code that does something like this
>     exists)

yup.

> 4. Resurrect the hotplug-remove code (exists, but probably very stale)

I don't even remember what that looks like.

> 5. Allow allocations for hugepages outside of the pool as long as the
>     process remains with it's locked_vm limits (patches were posted to
>     libhugetlbfs last Friday. will post to linux-mm tomorrow).

hm.


I'm not saying that we need to do memory hot-unplug immediately.  But the
overlaps between this and anti-frag and lumpiness are sufficient that I do
think that we need to work out how we'll implement hot-unplug, so we don't
screw ourselves up later on.

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