Messages in this thread | | | From | Nick Piggin <> | Subject | Re: [PATCH] SLUB: revert direct page allocator pass through | Date | Tue, 3 Feb 2009 12:33:39 +1100 |
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On Tuesday 27 January 2009 04:17:28 Christoph Lameter wrote: > On Sat, 24 Jan 2009, Nick Piggin wrote:
> > Other ones which could be changed but could introduce regressions are > > watermarks, buddy merging, and struct page error checking and setup. > > Isnt it possible to defer that (queuing them (sigh)).
If you defer it then you lose merge opportunities and effectively increase the rate of fragmentation.
> A bitmap could be > used to avoid queuing and may even allow fully concurrent allocations > without locks. Use a counter to check watermarks once in a while.
Bitmap? Involving locks or atomic operations, right?
> > (I did make that patch to enable refcounting to be avoided FWIW, which > > avoids a couple of atomic operations, but I don't think it brought > > performance up too much, but I still intend to dust it off at some > > point). > > Well if the page stays with a refcount of one then we do not need to check > the refcount at all but just push it in an out of some queue / bitmap or > something.
I sent you the patch but I don't think you ever came back with numbers. It's trivial, you just can avoid the put_page_testzero if the caller does not need refcounting and the refcount remains at 0 (has to remain 0, not 1, because of speculative page references).
The page refcounting layer lives on top of the buddy/queueing/etc layers, so the same technique works no matter what the underlying allocator looks like.
The only reason I didn't merge it is that it added another branch. I wanted to rework the APIs a little bit to avoid it.
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