From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754219AbaFKCKO (ORCPT ); Tue, 10 Jun 2014 22:10:14 -0400 Received: from mail-pb0-f51.google.com ([209.85.160.51]:47818 "EHLO mail-pb0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753120AbaFKCKM (ORCPT ); Tue, 10 Jun 2014 22:10:12 -0400 Message-ID: <1402452521.28433.26.camel@debian> Subject: Re: [PATCH] mm/vmscan.c: avoid recording the original scan targets in shrink_lruvec() From: Chen Yucong To: Andrew Morton Cc: mgorman@suse.de, mhocko@suse.cz, hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Wed, 11 Jun 2014 10:08:41 +0800 In-Reply-To: <20140610163338.5b463c5884c4c7e3f1b948e2@linux-foundation.org> References: <1402320436-22270-1-git-send-email-slaoub@gmail.com> <20140610163338.5b463c5884c4c7e3f1b948e2@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4-3 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2014-06-10 at 16:33 -0700, Andrew Morton wrote: > On Mon, 9 Jun 2014 21:27:16 +0800 Chen Yucong wrote: > > > Via https://lkml.org/lkml/2013/4/10/334 , we can find that recording the > > original scan targets introduces extra 40 bytes on the stack. This patch > > is able to avoid this situation and the call to memcpy(). At the same time, > > it does not change the relative design idea. > > > > ratio = original_nr_file / original_nr_anon; > > > > If (nr_file > nr_anon), then ratio = (nr_file - x) / nr_anon. > > x = nr_file - ratio * nr_anon; > > > > if (nr_file <= nr_anon), then ratio = nr_file / (nr_anon - x). > > x = nr_anon - nr_file / ratio; > > > > ... > > > > Are you sure this is an equivalent-to-before change? If so, then I > can't immediately see why :( > The relative design idea is to keep ratio == scan_target[anon] : scan_target[file] == really_scanned_num[anon] : really_scanned_num[file] The original implementation is ratio == (scan_target[anon] * percentage_anon) / (scan_target[file] * percentage_file) To keep the original ratio, percentage_anon should equal to percentage_file. In other word, we need to calculate the difference value between percentage_anon and percentage_file, we also have to record the original scan targets for this. Instead, we can calculate the *ratio* at the beginning of shrink_lruvec(). As a result, this can avoid introducing the extra 40 bytes. In short, we have the same goal: keep the same *ratio* from beginning to end. thx! cyc From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f172.google.com (mail-pd0-f172.google.com [209.85.192.172]) by kanga.kvack.org (Postfix) with ESMTP id BAF746B012E for ; Tue, 10 Jun 2014 22:10:13 -0400 (EDT) Received: by mail-pd0-f172.google.com with SMTP id fp1so6716348pdb.3 for ; Tue, 10 Jun 2014 19:10:13 -0700 (PDT) Received: from mail-pb0-x233.google.com (mail-pb0-x233.google.com [2607:f8b0:400e:c01::233]) by mx.google.com with ESMTPS id rq4si4849407pac.66.2014.06.10.19.10.12 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 10 Jun 2014 19:10:12 -0700 (PDT) Received: by mail-pb0-f51.google.com with SMTP id rp16so1447005pbb.38 for ; Tue, 10 Jun 2014 19:10:12 -0700 (PDT) Message-ID: <1402452521.28433.26.camel@debian> Subject: Re: [PATCH] mm/vmscan.c: avoid recording the original scan targets in shrink_lruvec() From: Chen Yucong Date: Wed, 11 Jun 2014 10:08:41 +0800 In-Reply-To: <20140610163338.5b463c5884c4c7e3f1b948e2@linux-foundation.org> References: <1402320436-22270-1-git-send-email-slaoub@gmail.com> <20140610163338.5b463c5884c4c7e3f1b948e2@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: mgorman@suse.de, mhocko@suse.cz, hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, 2014-06-10 at 16:33 -0700, Andrew Morton wrote: > On Mon, 9 Jun 2014 21:27:16 +0800 Chen Yucong wrote: > > > Via https://lkml.org/lkml/2013/4/10/334 , we can find that recording the > > original scan targets introduces extra 40 bytes on the stack. This patch > > is able to avoid this situation and the call to memcpy(). At the same time, > > it does not change the relative design idea. > > > > ratio = original_nr_file / original_nr_anon; > > > > If (nr_file > nr_anon), then ratio = (nr_file - x) / nr_anon. > > x = nr_file - ratio * nr_anon; > > > > if (nr_file <= nr_anon), then ratio = nr_file / (nr_anon - x). > > x = nr_anon - nr_file / ratio; > > > > ... > > > > Are you sure this is an equivalent-to-before change? If so, then I > can't immediately see why :( > The relative design idea is to keep ratio == scan_target[anon] : scan_target[file] == really_scanned_num[anon] : really_scanned_num[file] The original implementation is ratio == (scan_target[anon] * percentage_anon) / (scan_target[file] * percentage_file) To keep the original ratio, percentage_anon should equal to percentage_file. In other word, we need to calculate the difference value between percentage_anon and percentage_file, we also have to record the original scan targets for this. Instead, we can calculate the *ratio* at the beginning of shrink_lruvec(). As a result, this can avoid introducing the extra 40 bytes. In short, we have the same goal: keep the same *ratio* from beginning to end. thx! cyc -- 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