From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933871AbXLPOpU (ORCPT ); Sun, 16 Dec 2007 09:45:20 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763253AbXLPOpI (ORCPT ); Sun, 16 Dec 2007 09:45:08 -0500 Received: from gw1.cosmosbay.com ([86.65.150.130]:35334 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757542AbXLPOpH (ORCPT ); Sun, 16 Dec 2007 09:45:07 -0500 Message-ID: <476539D5.7050305@cosmosbay.com> Date: Sun, 16 Dec 2007 15:44:37 +0100 From: Eric Dumazet User-Agent: Thunderbird 2.0.0.9 (Windows/20071031) MIME-Version: 1.0 To: Adrian Bunk CC: Matt Mackall , Andrew Morton , Linux kernel Subject: Re: [RANDOM] Move two variables to read_mostly section to save memory References: <47650FBD.2060209@cosmosbay.com> <20071216130028.GB14233@stusta.de> In-Reply-To: <20071216130028.GB14233@stusta.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-1.6 (gw1.cosmosbay.com [86.65.150.130]); Sun, 16 Dec 2007 15:44:45 +0100 (CET) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Adrian Bunk a écrit : > On Sun, Dec 16, 2007 at 12:45:01PM +0100, Eric Dumazet wrote: >> While examining vmlinux namelist on i686, I noticed : >> >> c0581300 D random_table >> c0581480 d input_pool >> c0581580 d random_read_wakeup_thresh >> c0581584 d random_write_wakeup_thresh >> c0581600 d blocking_pool >> >> That means that the two integers random_read_wakeup_thresh and >> random_write_wakeup_thresh use a full cache entry (128 bytes). >> >> Moving them to read_mostly section can shrinks vmlinux by 120 bytes. >> >> # size vmlinux* >> text data bss dec hex filename >> 4835553 450210 610304 5896067 59f783 vmlinux.after_patch >> 4835553 450330 610304 5896187 59f7fb vmlinux.before_patch >> >> Signed-off-by: Eric Dumazet > >> diff --git a/drivers/char/random.c b/drivers/char/random.c >> index 5fee056..af48e86 100644 >> --- a/drivers/char/random.c >> +++ b/drivers/char/random.c >> @@ -256,14 +256,14 @@ >> * The minimum number of bits of entropy before we wake up a read on >> * /dev/random. Should be enough to do a significant reseed. >> */ >> -static int random_read_wakeup_thresh = 64; >> +static int random_read_wakeup_thresh __read_mostly = 64; >> >> /* >> * If the entropy count falls under this number of bits, then we >> * should wake up processes which are selecting or polling on write >> * access to /dev/random. >> */ >> -static int random_write_wakeup_thresh = 128; >> +static int random_write_wakeup_thresh __read_mostly = 128; > > Please never ever do such ugly and unmaintainable micro-optimizations in > the code unless you can show a measurable performance improvement of the > kernel. You seem to to be confused between speed micro-otimizations and memory savings. This patch has nothing to do about a speed optimization. Here, no tradeoff justify a "measurable performance improvement" study. I copied this patch to you because your recent proposal to remove read_mostly from linux kernel. Only you find read_mostly ugly and unmaintanable. I find it way more usefull than "static" attributes. I find 120 bytes is a measurable gain, thank you.