From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 23 Nov 2005 11:55:45 -0800 From: Andrew Morton Subject: Re: [PATCH]: Free pages from local pcp lists under tight memory conditions Message-Id: <20051123115545.69087adf.akpm@osdl.org> In-Reply-To: <1132775194.25086.54.camel@akash.sc.intel.com> References: <20051122161000.A22430@unix-os.sc.intel.com> <1132775194.25086.54.camel@akash.sc.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Rohit Seth Cc: clameter@engr.sgi.com, torvalds@osdl.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: Rohit Seth wrote: > > On Wed, 2005-11-23 at 11:30 -0800, Christoph Lameter wrote: > > On Tue, 22 Nov 2005, Rohit Seth wrote: > > > > > [PATCH]: This patch free pages (pcp->batch from each list at a time) from > > > local pcp lists when a higher order allocation request is not able to > > > get serviced from global free_list. > > > > Ummm.. One controversial idea: How about removing the complete pcp > > subsystem? Last time we disabled pcps we saw that the effect > > that it had was within noise ratio on AIM7. The lru lock taken without > > pcp is in the local zone and thus rarely contended. > > Oh please stop. > > This per_cpu_pagelist is one great logic that has got added in > allocator. Besides providing pages without the need to acquire the zone > lock, it is one single main reason the coloring effect is drastically > reduced in 2.6 (over 2.4) based kernels. > hm. Before it was merged in 2.5.x, the feature was very marginal from a performance POV in my testing on 4-way. I was able to demonstrate a large (~60%?) speedup in one microbenckmark which consisted of four processes writing 16k to a file and truncating it back to zero again. That gain came from the cache warmth effect, which is the other benefit which these cpu-local pages are supposed to provide. I don't think Martin was able to demonstrate much benefit from the lock contention reduction on 16-way NUMAQ either. So I dithered for months and it was a marginal merge, so it's appropriate to justify the continued presence of the code. We didn't measure for any coloring effects though. In fact, I didn't know that this feature actually provided any benefit in that area. -- 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