Messages in this thread | | | 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 |
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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
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