From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3D8F3C19759 for ; Wed, 7 Aug 2019 07:51:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0ED7222BED for ; Wed, 7 Aug 2019 07:51:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565164265; bh=5wRiz4FExZkKXNGm8O7ahIm0Q7LR8mJUis5fwzYmNzg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=urOcKhx5SoWggklJ5wx+M+9+XgLJ+kDUp6E5YJ3wbcAkdabU/p24nR/WHVtyqLOS5 aPM9slvPOVU5sNFs3PJKaBoE4XWF7LmTm0162LByVf0MEefWBqnU6bjyiujVtJHWKK Lrx4IGXAf+sU+fcy5hiRxXoW64ZdzZVcLJpC2zso= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387472AbfHGHvD (ORCPT ); Wed, 7 Aug 2019 03:51:03 -0400 Received: from mx2.suse.de ([195.135.220.15]:35212 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727331AbfHGHvD (ORCPT ); Wed, 7 Aug 2019 03:51:03 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 42D39AFDD; Wed, 7 Aug 2019 07:51:02 +0000 (UTC) Date: Wed, 7 Aug 2019 09:51:01 +0200 From: Michal Hocko To: Wei Yang Cc: Vlastimil Babka , akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/mmap.c: refine data locality of find_vma_prev Message-ID: <20190807075101.GN11812@dhcp22.suse.cz> References: <20190806081123.22334-1-richardw.yang@linux.intel.com> <3e57ba64-732b-d5be-1ad6-eecc731ef405@suse.cz> <20190807003109.GB24750@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190807003109.GB24750@richard> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 07-08-19 08:31:09, Wei Yang wrote: > On Tue, Aug 06, 2019 at 11:29:52AM +0200, Vlastimil Babka wrote: > >On 8/6/19 10:11 AM, Wei Yang wrote: > >> When addr is out of the range of the whole rb_tree, pprev will points to > >> the biggest node. find_vma_prev gets is by going through the right most > > > >s/biggest/last/ ? or right-most? > > > >> node of the tree. > >> > >> Since only the last node is the one it is looking for, it is not > >> necessary to assign pprev to those middle stage nodes. By assigning > >> pprev to the last node directly, it tries to improve the function > >> locality a little. > > > >In the end, it will always write to the cacheline of pprev. The caller has most > >likely have it on stack, so it's already hot, and there's no other CPU stealing > >it. So I don't understand where the improved locality comes from. The compiler > >can also optimize the patched code so the assembly is identical to the previous > >code, or vice versa. Did you check for differences? > > Vlastimil > > Thanks for your comment. > > I believe you get a point. I may not use the word locality. This patch tries > to reduce some unnecessary assignment of pprev. > > Original code would assign the value on each node during iteration, this is > what I want to reduce. Is there any measurable difference (on micro benchmarks or regular workloads)? -- Michal Hocko SUSE Labs