Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759606AbXE2Q7a (ORCPT ); Tue, 29 May 2007 12:59:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751790AbXE2Q7X (ORCPT ); Tue, 29 May 2007 12:59:23 -0400 Received: from mx1.redhat.com ([66.187.233.31]:44534 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751180AbXE2Q7W (ORCPT ); Tue, 29 May 2007 12:59:22 -0400 Message-ID: <465C5BE0.4090903@redhat.com> Date: Tue, 29 May 2007 12:59:12 -0400 From: Rik van Riel Organization: Red Hat, Inc User-Agent: Thunderbird 1.5.0.7 (X11/20061008) MIME-Version: 1.0 To: Nick Piggin CC: Linus Torvalds , linux-kernel , linux-mm , Andrew Morton , Ulrich Drepper , Jakub Jelinek Subject: Re: [PATCH] MM: implement MADV_FREE lazy freeing of anonymous memory References: <4632D0EF.9050701@redhat.com> <463B108C.10602@yahoo.com.au> In-Reply-To: <463B108C.10602@yahoo.com.au> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1403 Lines: 33 Nick Piggin wrote: > Rik van Riel wrote: >> With lazy freeing of anonymous pages through MADV_FREE, performance of >> the MySQL sysbench workload more than doubles on my quad-core system. > > OK, I've run some tests on a 16 core Opteron system, both sysbench with > MySQL 5.33 (set up as described in the freebsd vs linux page), and with > ebizzy. > > What I found is that, on this system, MADV_FREE performance improvement > was in the noise when you look at it on top of the MADV_DONTNEED glibc > and down_read(mmap_sem) patch in sysbench. It turns out that setting the pte accessed bit in hardware can apparently take a few thousand CPU cycles - 3000 cycles is the number I've heard for one CPU family. This is a similar number of cycles as is needed to zero out a page. Giving a cache hot page to userspace could cancel out the rest of the cost of the page fault handling. Lets stick with the simpler MADV_DONTNEED code for now and save the page flag for something else... -- Politics is the struggle between those who want to make their country the best in the world, and those who believe it already is. Each group calls the other unpatriotic. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/