From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753989AbXDVCg7 (ORCPT ); Sat, 21 Apr 2007 22:36:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753990AbXDVCg7 (ORCPT ); Sat, 21 Apr 2007 22:36:59 -0400 Received: from smtp101.mail.mud.yahoo.com ([209.191.85.211]:33685 "HELO smtp101.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753989AbXDVCg6 (ORCPT ); Sat, 21 Apr 2007 22:36:58 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:X-YMail-OSG:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=vRUCtym8LR3Z8d9SgqY4SDYU30ZsI0p36A/5uPlcjFIX9JSDnc73bLdjG3tbgbPTMcXPqOI+fkugTkNN31uFx8ElsC647LvsoDyjzi2tqSTc96synXUu7ZntipOAyg1E9f0Cj7/8oV+GKCtFMT8UJ9E2H3EJRAudxREGicoj60E= ; X-YMail-OSG: L9jSUDEVM1lP4QyqqYnKJinPllcAv5P.rVk.9IJ0FDemEfl7q3cKZ87SVYMJETxypytHwbQhfg-- Message-ID: <462ACA40.8070407@yahoo.com.au> Date: Sun, 22 Apr 2007 12:36:48 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20051007 Debian/1.7.12-1 X-Accept-Language: en MIME-Version: 1.0 To: Rik van Riel CC: Andrew Morton , linux-kernel , linux-mm , shak Subject: Re: [PATCH] lazy freeing of memory through MADV_FREE References: <46247427.6000902@redhat.com> <20070420135715.f6e8e091.akpm@linux-foundation.org> <462932BE.4020005@redhat.com> <20070420150618.179d31a4.akpm@linux-foundation.org> <4629524C.5040302@redhat.com> In-Reply-To: <4629524C.5040302@redhat.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Rik van Riel wrote: > Andrew Morton wrote: > >> On Fri, 20 Apr 2007 17:38:06 -0400 >> Rik van Riel wrote: >> >>> Andrew Morton wrote: >>> >>>> I've also merged Nick's "mm: madvise avoid exclusive mmap_sem". >>>> >>>> - Nick's patch also will help this problem. It could be that your >>>> patch >>>> no longer offers a 2x speedup when combined with Nick's patch. >>>> >>>> It could well be that the combination of the two is even better, >>>> but it >>>> would be nice to firm that up a bit. >>> >>> I'll test that. >> >> >> Thanks. > > > Well, good news. > > It turns out that Nick's patch does not improve peak > performance much, but it does prevent the decline when > running with 16 threads on my quad core CPU! > > We _definately_ want both patches, there's a huge benefit > in having them both. > > Here are the transactions/seconds for each combination: > > vanilla new glibc madv_free kernel madv_free + mmap_sem > threads > > 1 610 609 596 545 > 2 1032 1136 1196 1200 > 4 1070 1128 2014 2024 > 8 1000 1088 1665 2087 > 16 779 1073 1310 1999 Is "new glibc" meaning MADV_DONTNEED + kernel with mmap_sem patch? The strange thing with your madv_free kernel is that it doesn't help single-threaded performance at all. So that work to avoid zeroing the new page is not a win at all there (maybe due to the cache effects I was worried about?). However MADV_FREE does improve scalability, which is interesting. The most likely reason I can see why that may be the case is that it avoids mmap_sem when faulting pages back in (I doubt it is due to avoiding the page allocator, but maybe?). So where is the down_write coming from in this workload, I wonder? Heap management? What syscalls? x86_64's rwsems are crap under heavy parallelism (even read-only), as I fixed in my recent generic rwsems patch. I don't expect MySQL to be such a mmap_sem microbenchmark, but I wonder how much this would help? What if we ran the private futexes patch to further cut down mmap_sem contention? -- SUSE Labs, Novell Inc.