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

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Date:	Sat, 2 May 2009 13:46:34 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	pavel@....cz, torvalds@...ux-foundation.org, jens.axboe@...cle.com,
	alan-jenkins@...fmail.co.uk, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH 3/3] PM/Hibernate: Use memory allocations to free memory

On Saturday 02 May 2009, Andrew Morton wrote:
> On Sat, 2 May 2009 00:29:38 +0200
> "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> 
> > From: Rafael J. Wysocki <rjw@...k.pl>
> > 
> > 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!
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