Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [RFC][PATCH 6/6] PM/Hibernate: Do not try to allocate too much memory too hard | Date | Sun, 17 May 2009 14:55:05 +0200 |
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On Sunday 17 May 2009, Wu Fengguang wrote: > Hi Rafael,
Hi,
> Sorry for being late.
No big deal.
> On Wed, May 13, 2009 at 04:42:17PM +0800, Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki <rjw@sisk.pl> > > > > We want to avoid attempting to free too much memory too hard during > > hibernation, so estimate the minimum size of the image to use as the > > lower limit for preallocating memory. > > > > The approach here is based on the (experimental) observation that we > > can't free more page frames than the sum of: > > > > * 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) > > It's a very good idea to count the numbers in a reverse way. > > > and even that is usually impossible to free in practice, because some > > of the pages reported as global_page_state(NR_SLAB_RECLAIMABLE) can't > > in fact be freed. It turns out, however, that if the sum of the > > above numbers is subtracted from the number of saveable pages in the > > system and the result is multiplied by 1.25, we get a suitable > > estimate of the minimum size of the image. > > However, the "*1.25" looks like a hack.
It's just an experimental value.
> We should really apply more constraints to the individual components. > > > Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> > > --- > > kernel/power/snapshot.c | 56 ++++++++++++++++++++++++++++++++++++++++++++---- > > 1 file changed, 52 insertions(+), 4 deletions(-) > > > > Index: linux-2.6/kernel/power/snapshot.c > > =================================================================== > > --- linux-2.6.orig/kernel/power/snapshot.c > > +++ linux-2.6/kernel/power/snapshot.c > > @@ -1213,6 +1213,49 @@ static void free_unnecessary_pages(void) > > } > > > > /** > > + * minimum_image_size - Estimate the minimum acceptable size of an image > > + * @saveable: The total number of saveable pages in the system. > > + * > > + * We want to avoid attempting to free too much memory too hard, so estimate the > > + * minimum acceptable size of a hibernation image to use as the lower limit for > > + * preallocating memory. > > + * > > + * The minimum size of the image is computed as > > + * > > + * ([number of saveable pages] - [number of pages we can free]) * 1.25 > > + * > > + * where the second term is the sum of reclaimable slab, anonymouns pages and > > + * active/inactive file pages. > > + * > > + * NOTE: It usually turns out that we can't really free all pages reported as > > + * reclaimable slab, so the number resulting from the subtraction alone is too > > + * low. Still, it seems reasonable to assume that this number is proportional > > + * to the total number of pages that cannot be freed, which leads to the > > + * formula above. The coefficient of proportinality in this formula, 1.25, has > > + * been determined experimentally. > > + */ > > +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?
> /* keep NR_ACTIVE_ANON */ > size += global_page_state(NR_INACTIVE_ANON);
Why exactly did you omit ACTIVE_ANON?
> /* 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.
Thanks, Rafael
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