linux-kernel - Re: [patch 5/9] Guest page hinting: mlocked pages.

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Message-Id: <1158224355.18478.26.camel@localhost>
Date:	Thu, 14 Sep 2006 10:59:15 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Zachary Amsden <zach@...are.com>
Cc:	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	akpm@...l.org, nickpiggin@...oo.com.au, frankeh@...son.ibm.com,
	rhim@...gateh.edu
Subject: Re: [patch 5/9] Guest page hinting: mlocked pages.

On Wed, 2006-09-13 at 18:22 -0700, Zachary Amsden wrote:
> Martin Schwidefsky wrote:
> > diff -urpN linux-2.6/mm/memory.c linux-2.6-patched/mm/memory.c
> > --- linux-2.6/mm/memory.c	2006-09-01 12:50:24.000000000 +0200
> > +++ linux-2.6-patched/mm/memory.c	2006-09-01 12:50:24.000000000 +0200
> > @@ -2523,6 +2523,31 @@ int make_pages_present(unsigned long add
> >  	BUG_ON(addr >= end);
> >  	BUG_ON(end > vma->vm_end);
> >  	len = (end+PAGE_SIZE-1)/PAGE_SIZE-addr/PAGE_SIZE;
> > +
> > +	if (page_host_discards() && (vma->vm_flags & VM_LOCKED)) {
> > +		int rlen = len;
> > +		ret = 0;
> > +		while (rlen > 0) {
> > +			struct page *page_refs[32];
> > +			int chunk, cret, i;
> > +
> > +			chunk = rlen < 32 ? rlen : 32;
> > +			cret = get_user_pages(current, current->mm, addr,
> > +					      chunk, write, 0,
> > +					      page_refs, NULL);
> > +			if (cret > 0) {
> > +				for (i = 0; i < cret; i++)
> > +					page_cache_release(page_refs[i]);
> > +				ret += cret;
> > +			}
> > +			if (cret < chunk)
> > +				return ret ? : cret;
> > +			addr += 32*PAGE_SIZE;
> > +			rlen -= 32;
> > +		}
> > +		return ret == len ? 0 : -1;
> > +	}
> > +
> >  	ret = get_user_pages(current, current->mm, addr,
> >  			len, write, 0, NULL, NULL);
> >  	if (ret < 0)
> >   
> 
> This seems like a bit of unneeded complexity.  Since you've already 
> changed get_user_pages, why not add a follow flag to release the page 
> cache, and simply pass it to get_user_pages, instead of trying to fetch 
> the page list back.  In particular, write and force arguments to 
> get_user_pages look very ripe for combining into a flags field.  Sure, 
> get_user_pages now has a bit more work to do, but it is already a 
> monster, and I think it would keep make_page_present much cleaner.

That makes sense. If we combine write and force the additional flag we
need won't hurt. I'll add this to my to-do list.

-- 
blue skies,
  Martin.

Martin Schwidefsky
Linux for zSeries Development & Services
IBM Deutschland Entwicklung GmbH

"Reality continues to ruin my life." - Calvin.


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