Re: [PATCH 3/3] PM/Hibernate: Use memory allocations to free memory

Rafael J. Wysocki
2009-05-02T11:46:34Z

On Saturday 02 May 2009, Andrew Morton wrote:
> On Sat, 2 May 2009 00:29:38 +0200
> "Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org> wrote:
>
> > From: Rafael J. Wysocki <rjw-KKrjLPT3xs0@public.gmane.org>
> >
> > Modify the hibernation memory shrinking code so that it will make
> > memory allocations to free memory instead of using an artificial
> > memory shrinking mechanism for that. Remove the shrinking of
> > memory from the suspend-to-RAM code, where it is not really
> > necessary. Finally, remove the no longer used memory shrinking
> > functions from mm/vmscan.c .
> >
> > ...
> >
> > +static long alloc_and_mark_pages(struct memory_bitmap *bm, long nr_pages)
> > {
> > - if (tmp > SHRINK_BITE)
> > - tmp = SHRINK_BITE;
> > - return shrink_all_memory(tmp);
> > + long nr_normal = 0;
> > +
> > + while (nr_pages-- > 0) {
> > + struct page *page;
> > +
> > + page = alloc_page(GFP_KERNEL | __GFP_HIGHMEM);
> > + if (!page)
> > + return -ENOMEM;
> > + memory_bm_set_bit(bm, page_to_pfn(page));
> > + if (!PageHighMem(page))
> > + nr_normal++;
> > + }
> > +
> > + return nr_normal;
> > }
>
> Do we need the bitmap? I expect we can just string all these pages
> onto a local list via page.lru. Would need to check that - the
> pageframe fields are quite overloaded.

This is the reason why we use the bitmaps for hibernation. :-)

> > ...
> >
> > +#define SHRINK_BITE 10000
> > + long size, highmem_size, ret;
> > +
> > + highmem_size = count_highmem_pages() - 2 * alloc_highmem;
> > + size = count_data_pages() + PAGES_FOR_IO + SPARE_PAGES
> > + - 2 * alloc_normal;
>
> It'd be nice if this head-spinning arithmetic were spelled out in a
> comment somewhere. There are rather a lot of magic-number heuristics
> in here.

Well, yeah. I'll try to write up something. :-)

> > tmp = size;
> > size += highmem_size;
> > for_each_populated_zone(zone) {
> > @@ -621,27 +671,39 @@ int swsusp_shrink_memory(void)
>
> All looks pretty sane to me.

Great, thanks for the comments!