From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 19 Aug 2008 12:25:10 +0200 From: Nick Piggin Subject: Re: [patch] mm: page allocator minor speedup Message-ID: <20080819102510.GD16446@wotan.suse.de> References: <20080818122428.GA9062@wotan.suse.de> <20080818122957.GE9062@wotan.suse.de> <84144f020808180657v2bdd5f76l4b0f1897c73ec0c0@mail.gmail.com> <20080819074911.GA10447@wotan.suse.de> <1219132301.7813.358.camel@penberg-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1219132301.7813.358.camel@penberg-laptop> Sender: owner-linux-mm@kvack.org Return-Path: To: Pekka Enberg Cc: Andrew Morton , Linux Memory Management List , Hugh Dickins , Christoph Lameter List-ID: On Tue, Aug 19, 2008 at 10:51:41AM +0300, Pekka Enberg wrote: > Hi Nick, > > On Mon, Aug 18, 2008 at 3:29 PM, Nick Piggin wrote: > > > > Now that we don't put a ZERO_PAGE in the pagetables any more, and the > > > > "remove PageReserved from core mm" patch has had a long time to mature, > > > > let's remove the page reserved logic from the allocator. > > > > > > > > This saves several branches and about 100 bytes in some important paths. > ??? > On Mon, Aug 18, 2008 at 04:57:00PM +0300, Pekka Enberg wrote: > > > Cool. Any numbers for this? > > ???On Tue, 2008-08-19 at 09:49 +0200, Nick Piggin wrote: > > No, no numbers. I expect it would be very difficult to measure because > > it probably only starts saving cycles when the workload exceeds L1I and/or > > the branch caches. > > OK, I am asking this because any improvements in the page allocator fast > paths are going to be a gain for SLUB intensive workloads as well. Right. "OLTP" is *very* cache and branch sensitive... but I doubt this would stand out from the noise. BTW. I have a patch somewhere that adds a new interface to the page allocator which avoids setting the page refcount. This way if you're careful you can free the page after use without the expensive atomic_dec_and_test & branch. I didn't quite get it into a form that I like (would have required some more extensive page allocator rework). But if you're interested in numbers, then what I had should be enough to get an idea... Remember to give SLAB the same advantage too ;)! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org