linux-kernel - Re: [PATCH] lazy freeing of memory through MADV

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Date:	Fri, 20 Apr 2007 15:06:18 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] lazy freeing of memory through MADV_FREE

On Fri, 20 Apr 2007 17:38:06 -0400
Rik van Riel <riel@...hat.com> wrote:

> Andrew Morton wrote:
> 
> > I've also merged Nick's "mm: madvise avoid exclusive mmap_sem".
> > 
> > - Nick's patch also will help this problem.  It could be that your patch
> >   no longer offers a 2x speedup when combined with Nick's patch.
> > 
> >   It could well be that the combination of the two is even better, but it
> >   would be nice to firm that up a bit.  
> 
> I'll test that.

Thanks.

> >   I do go on about that.  But we're adding page flags at about one per
> >   year, and when we run out we're screwed - we'll need to grow the
> >   pageframe.
> 
> If you want, I can take a look at folding this into the
> ->mapping pointer.  I can guarantee you it won't be
> pretty, though :)

Well, let's see how fugly it ends up looking?

> > - I need to update your patch for Nick's patch.  Please confirm that
> >   down_read(mmap_sem) is sufficient for MADV_FREE.
> 
> It is.  MADV_FREE needs no more protection than MADV_DONTNEED.
> 
> > Stylistic nit:
> > 
> >> +	if (PageLazyFree(page) && !migration) {
> >> +		/* There is new data in the page.  Reinstate it. */
> >> +		if (unlikely(pte_dirty(pteval))) {
> >> +			set_pte_at(mm, address, pte, pteval);
> >> +			ret = SWAP_FAIL;
> >> +			goto out_unmap;
> >> +		}
> > 
> > The comment should be inside the second `if' statement.  As it is, It
> > looks like we reinstate the page if (PageLazyFree(page) && !migration).
> 
> Want me to move it?

I did that, thanks.
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