From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754254AbZEQQyV (ORCPT ); Sun, 17 May 2009 12:54:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753042AbZEQQyJ (ORCPT ); Sun, 17 May 2009 12:54:09 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:47684 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752786AbZEQQyH (ORCPT ); Sun, 17 May 2009 12:54:07 -0400 From: "Rafael J. Wysocki" To: Wu Fengguang Subject: Re: [RFC][PATCH 6/6] PM/Hibernate: Do not try to allocate too much memory too hard Date: Sun, 17 May 2009 18:53:37 +0200 User-Agent: KMail/1.11.2 (Linux/2.6.30-rc5-rjw; KDE/4.2.2; x86_64; ; ) Cc: pm list , Andrew Morton , LKML , Pavel Machek , Nigel Cunningham , David Rientjes , "linux-mm@kvack.org" References: <200905070040.08561.rjw@sisk.pl> <200905171455.06120.rjw@sisk.pl> <20090517140712.GE3254@localhost> In-Reply-To: <20090517140712.GE3254@localhost> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200905171853.38028.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sunday 17 May 2009, Wu Fengguang wrote: > On Sun, May 17, 2009 at 08:55:05PM +0800, Rafael J. Wysocki wrote: > > On Sunday 17 May 2009, Wu Fengguang wrote: > > > > > +static unsigned long minimum_image_size(unsigned long saveable) > > > > +{ > > > > + unsigned long size; > > > > + > > > > + /* Compute the number of saveable pages we can free. */ > > > > + size = global_page_state(NR_SLAB_RECLAIMABLE) > > > > + + global_page_state(NR_ACTIVE_ANON) > > > > + + global_page_state(NR_INACTIVE_ANON) > > > > + + global_page_state(NR_ACTIVE_FILE) > > > > + + global_page_state(NR_INACTIVE_FILE); > > > > > > For example, we could drop the 1.25 ratio and calculate the above > > > reclaimable size with more meaningful constraints: > > > > > > /* slabs are not easy to reclaim */ > > > size = global_page_state(NR_SLAB_RECLAIMABLE) / 2; > > > > Why 1/2? > > Also a very coarse value: > - we don't want to stress icache/dcache too much > (unless they grow too large) > - my experience was that the icache/dcache are scanned in a slower > pace than lru pages. That doesn't really matter, we're talking about the minimum image size. > - most importantly, inside the NR_SLAB_RECLAIMABLE pages, maybe half > of the pages are actually *in use* and cannot be freed: > % cat /proc/sys/fs/inode-nr > 30450 16605 > % cat /proc/sys/fs/dentry-state > 41598 35731 45 0 0 0 > See? More than half entries are in-use. Sure many of them will actually > become unused when dentries are freed, but in the mean time the internal > fragmentations in the slabs can go up. > > > > /* keep NR_ACTIVE_ANON */ > > > size += global_page_state(NR_INACTIVE_ANON); > > > > Why exactly did you omit ACTIVE_ANON? > > To keep the "core working set" :) > > > > /* keep mapped files */ > > > size += global_page_state(NR_ACTIVE_FILE); > > > size += global_page_state(NR_INACTIVE_FILE); > > > size -= global_page_state(NR_FILE_MAPPED); > > > > > > That restores the hard core working set logic in the reverse way ;) > > > > I think the 1/2 factor for NR_SLAB_RECLAIMABLE may be too high in some cases, > > but I'm going to check that. > > Yes, after updatedb. In that case simple magics numbers may not help. > In that case we should really first call shrink_slab() in a loop to > cut down the slab pages to a sane number. Unfortunately your formula above doesn't also work after running shrink_all_memory(), because the number given by it is still too high in that case. The resulting minimum image size is then too low. OTOH, the number computed in accordance with my original 1.25 * () formula is fine in all cases I have checked (it actuall would be sufficient to take 1.2 * , but the difference is not really significant). I don't think we can derive everything directly from the statistics collected by the mm subsystem. Thanks, Rafael