From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933644AbXLPNAf (ORCPT ); Sun, 16 Dec 2007 08:00:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763639AbXLPNAZ (ORCPT ); Sun, 16 Dec 2007 08:00:25 -0500 Received: from emailhub.stusta.mhn.de ([141.84.69.5]:58213 "EHLO mailhub.stusta.mhn.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1759629AbXLPNAY (ORCPT ); Sun, 16 Dec 2007 08:00:24 -0500 Date: Sun, 16 Dec 2007 14:00:28 +0100 From: Adrian Bunk To: Eric Dumazet Cc: Matt Mackall , Andrew Morton , Linux kernel Subject: Re: [RANDOM] Move two variables to read_mostly section to save memory Message-ID: <20071216130028.GB14233@stusta.de> References: <47650FBD.2060209@cosmosbay.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <47650FBD.2060209@cosmosbay.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. cu Adrian -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed