From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965287AbXDWARI (ORCPT ); Sun, 22 Apr 2007 20:17:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965656AbXDWARI (ORCPT ); Sun, 22 Apr 2007 20:17:08 -0400 Received: from smtp103.mail.mud.yahoo.com ([209.191.85.213]:47429 "HELO smtp103.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S965287AbXDWARH (ORCPT ); Sun, 22 Apr 2007 20:17:07 -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=sKkVQDp6SLS9kbQWi3tz4kpYEMXh50bL/IQocBGUjEkIhuDFCsT47l/nRwWi0vkcm6Ch6oiUuPPp6xYH+bB+/cxeuZCZsm51tf5IukORCoenMH5+qWBCY5zoLjmdrcmZW1sJ9Upx5ifOgymJcCZ5ANEcwV60ymH4qiShj4dR8gc= ; X-YMail-OSG: 2df_SA0VM1nlF2ju13FSuF.Qb5zTorn1rpK_7JlI_ml50KlzBGz_JsbRkGxirkdWCo6P8Smfcw-- Message-ID: <462BFAF3.4040509@yahoo.com.au> Date: Mon, 23 Apr 2007 10:16:51 +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> <462ACA40.8070407@yahoo.com.au> <462B0156.9020407@redhat.com> In-Reply-To: <462B0156.9020407@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: > Nick Piggin wrote: > >> Rik van Riel wrote: >>> 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? > > > No, that's just the glibc change, with a vanilla kernel. OK. That would be interesting to see with the mmap_sem change, because that should increase scalability. > The third column is glibc change + mmap_sem patch. > > The fourth column has your patch in it, too. > >> 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?). > > > Well, your patch causes the performance to drop from > 596 transactions/second to 545. Your patch is the only > difference between the third and the fourth column. Yeah. That's funny, because it means either there is some contention on the mmap_sem (or ptl) at 1 thread, or that my patch alters the uncontended performance. >> 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? > > > I wonder if the increased parallelism simply caused > more cache line bouncing, with bounces happening in > some inner loop instead of an outer loop. > > Btw, it is quite possible that the MySQL sysbench > thing gives different results on your system. It > would be good to know what it does on a real SMP > system, vs. a single quad-core chip :) > > Other architectures would be interesting to know, > too. I don't see why parallelism should come into it at 1 thread, unless MySQL is parallelising individual transactions. Anyway, I'll try to do some more digging. -- SUSE Labs, Novell Inc.