When I was posting CMA, it had been suggested to create a new migration type
dedicated to contiguous allocations. I think I already did that and thanks to
this new migration type we have (i) an area of memory that only accepts movable
and reclaimable pages and
Andi Kleen <andi.kleen@xxxxxxxxx> wrote:
Aka highmem next generation :-(
On Fri, Oct 29, 2010 at 11:59:00AM +0100, KAMEZAWA Hiroyuki wrote:
yes. But Nick's new shrink_slab() may be a new help even without
new zone.
On Fri, 29 Oct 2010 14:29:28 +0200, Andi Kleen <andi.kleen@xxxxxxxxx> wrote:
You would really need callbacks into lots of code. Christoph
used to have some patches for directed shrink of dcache/icache,
but they are currently not on the table.
I don't think Nick's patch does that, he simply optimizes the existing
shrinker (which in practice tends to not shrink a lot) to be a bit
less wasteful.
The coverage will never be 100% in any case. So you always have to
make a choice between movable or fully usable. That's essentially
highmem with most of its problems.
Yep.
(ii) is used only if all other (non-reserved) pages have
been allocated.
That will be near always the case after some uptime, as memory fills up
with caches. Unless you do early reclaim?
Hmm... true. Still the point remains that only movable and reclaimable pages are
allowed in the marked regions. This in effect means that from unmovable pages
point of view, the area is unusable but I havn't thought of any other way to
guarantee that because of fragmentation, long sequence of free/movable/reclaimable
pages is available.
memory migration always do work with alloc_page() for getting migration target
pages. So, memory will be reclaimed if filled by cache.
Was talking about that paragraph CMA, not your patch.
If I understand it correctly CMA wants to define
a new zone which is somehow similar to movable, but only sometimes used
when another zone is full (which is the usual state in normal
operation actually)
It was unclear to me how this was all supposed to work. At least
as described in the paragraph it cannot I think.
It's not a new zone, just a new migrate type. I haven't tested it yet,
but the idea is that once pageblock's migrate type is set to this
new MIGRATE_CMA type, buddy allocator never changes it and in
fallback list it's put on the end of entries for MIGRATE_RECLAIMABLE
and MIGRATE_MOVABLE.
If I got everything right, this means that pages from MIGRATE_CMA pageblocks
are available for movable and reclaimable allocations but not for unmovable.
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