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

[Hugh Dickins <hugh@veritas.com>]

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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