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

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Message-Id: <20061205101629.5cb78828.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 5 Dec 2006 10:16:29 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	akpm@...l.org, clameter@....com, apw@...dowen.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that
 may be migrated


Hi, your plan looks good to me.
some comments.

On Mon, 4 Dec 2006 23:45:32 +0000 (GMT)
Mel Gorman <mel@....ul.ie> wrote:
> 1. Use lumpy-reclaim to intelligently reclaim contigous pages. The same
>     logic can be used to reclaim within a PFN range
> 2. Merge anti-frag to help high-order allocations, hugetlbpage
>     allocations and freeing up SPARSEMEM sections of memory
For freeing up SPARSEMEM sections of memory ? 
It looks that you assumes MAX_ORDER_NR_PAGES equals to PAGES_PER_SECTION.
plz don't assume that when you talk about generic arch code.

> 3. Anti-frag includes support for page flags that affected a MAX_ORDER block
>     of pages. These flags can be used to mark a section of memory that should
>     not be allocated from. This is of interest to both hugetlb page allocatoin
>     and memory hot-remove. Use the flags to mark a MAX_ORDER_NR_PAGES that
>     is currently being freed up and shouldn't be allocated. 

> 4. Use anti-frag fallback logic to bias unmovable allocations to the lower
>     PFNs.
I think this can be one of the most diffcult things ;)

> 5. Add arch support where possible for offlining sections of memory that
>     can be powered down.
I had a patch for ACPI-memory-hot-unplug, which ties memory sections to memory
chunk on ACPI.

> 6. Add arch support where possible to power down a DIMM when the memory
>     sections that make it up have been offlined. This is an extenstion of
>     step 5 only.
> 7. Add a zone that only allows __GFP_MOVABLE allocations so that
>     sections can 100% be reclaimed and powered-down
> 8. Allow nodes to only have a zone for __GFP_MOVABLE allocations so that
>     whole nodes can be offlined.
> 
I (numa-node-hotplug) needs 7 and 8 basically. And Other people may not.
IMHO:
For DIMM unplug, I suspect that we'll finally divide memory to core-memory and
hot-pluggable by pgdat even on SMP. If we use pgdat for that purpose, almost all
necessary infrastructure(statistics ,etc..) is ready. 
But if we find better way, it's good.

-Kame

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