linux-kernel - Re: [PATCH] Move memory controller allocations to their own slabs (v3)

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Date:	Fri, 14 Mar 2008 11:16:09 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelianov <xemul@...nvz.org>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] Move memory controller allocations to their own slabs
 (v3)

On Fri, 14 Mar 2008, KAMEZAWA Hiroyuki wrote:
> At first, in my understanding,
> - MOVABLE is for migratable pages. (so, not for kernel objects.)
> - RECLAIMABLE is for reclaimable kernel objects. (for slab etc..)
> 
> All reclaimable objects are not necessary to be always reclaimable but
> some amount of RECLAIMABLE objects (not all) should be recraimable easily.
> For example, some of dentry-cache, inode-cache is reclaimable because *unused*
> objects are cached.
> 
> When it comes to page_cgroup, *all* objects has dependency to pages which are
> assigned to.  And user pages are reclaimable.
> There is a similar object....the radix tree. radix-tree's node is allocated as
> RECLAIMABLE object.
> 
> So I think it makes sense to changing page_cgroup to be reclaimable.
> 
> But final decision should be done by how fragmentation avoidance works.
> It's good to test "how many hugepages can be allocated dynamically" when we
> make page_cgroup to be GFP_RECAIMABLE 

I agree with you on all points.  No need for it to be done in the same
patch as Balbir's, but yes, __GFP_RECLAIMABLE appears to be appropriate
for the page_cgroup kmem_cache.

(I think it's a better fit than for the radix_tree_node cache: though
the common pagecache usage of the radix_tree implies that its nodes
are reclaimable, I can't see why radix_tree nodes would intrinsically
be reclaimable.  If a significant non-reclaimable user of radix-tree
comes on the scene, I'd expect us to change that assumption.)

Hugh
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