From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 76E8A6B0055 for ; Sun, 17 May 2009 10:07:36 -0400 (EDT) Date: Sun, 17 May 2009 22:07:12 +0800 From: Wu Fengguang Subject: Re: [RFC][PATCH 6/6] PM/Hibernate: Do not try to allocate too much memory too hard Message-ID: <20090517140712.GE3254@localhost> References: <200905070040.08561.rjw@sisk.pl> <200905131042.18137.rjw@sisk.pl> <20090517120613.GB3254@localhost> <200905171455.06120.rjw@sisk.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200905171455.06120.rjw@sisk.pl> Sender: owner-linux-mm@kvack.org To: "Rafael J. Wysocki" Cc: pm list , Andrew Morton , LKML , Pavel Machek , Nigel Cunningham , David Rientjes , "linux-mm@kvack.org" List-ID: 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. - 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. Thanks, Fengguang -- 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