linux-kernel - Re: [patch] mm: dirty page tracking race fix

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Date:	Mon, 18 Aug 2008 18:03:57 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Nick Piggin <npiggin@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hugh@...itas.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] mm: dirty page tracking race fix

On Monday 18 August 2008 17:49, Peter Zijlstra wrote:
> On Mon, 2008-08-18 at 07:38 +0200, Nick Piggin wrote:

> > It's possible to retain this optimization for page_referenced and
> > try_to_unmap.
>
> s/synch/sync/ ?
>
> we use sync all over the kernel to mean synchonous, so why are you
> inventing a new shorthand?

Mmm, we also use synch all over the kernel to mean synchronous,
including in mm/, so I'm not inventing a new shorthand. sync I
see is more common, but it's not something anybody would get
confused about is it?

>
> Anyway, still
>
> Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

Thanks.


> > Signed-off-by: Nick Piggin <npiggin@...e.de>
> > ---
> > Index: linux-2.6/include/linux/rmap.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/rmap.h
> > +++ linux-2.6/include/linux/rmap.h
> > @@ -102,7 +102,7 @@ int try_to_unmap(struct page *, int igno
> >   * Called from mm/filemap_xip.c to unmap empty zero page
> >   */
> >  pte_t *page_check_address(struct page *, struct mm_struct *,
> > -				unsigned long, spinlock_t **);
> > +				unsigned long, spinlock_t **, int);
> >
> >  /*
> >   * Used by swapoff to help locate where page is expected in vma.
> > Index: linux-2.6/mm/filemap_xip.c
> > ===================================================================
> > --- linux-2.6.orig/mm/filemap_xip.c
> > +++ linux-2.6/mm/filemap_xip.c
> > @@ -185,7 +185,7 @@ __xip_unmap (struct address_space * mapp
> >  		address = vma->vm_start +
> >  			((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
> >  		BUG_ON(address < vma->vm_start || address >= vma->vm_end);
> > -		pte = page_check_address(page, mm, address, &ptl);
> > +		pte = page_check_address(page, mm, address, &ptl, 1);
> >  		if (pte) {
> >  			/* Nuke the page table entry. */
> >  			flush_cache_page(vma, address, pte_pfn(*pte));
> > Index: linux-2.6/mm/rmap.c
> > ===================================================================
> > --- linux-2.6.orig/mm/rmap.c
> > +++ linux-2.6/mm/rmap.c
> > @@ -224,10 +224,14 @@ unsigned long page_address_in_vma(struct
> >  /*
> >   * Check that @page is mapped at @address into @mm.
> >   *
> > + * If @synch is false, page_check_address may perform a racy check to
> > avoid + * the page table lock when the pte is not present (helpful when
> > reclaiming + * highly shared pages).
> > + *
> >   * On success returns with pte mapped and locked.
> >   */
> >  pte_t *page_check_address(struct page *page, struct mm_struct *mm,
> > -			  unsigned long address, spinlock_t **ptlp)
> > +			  unsigned long address, spinlock_t **ptlp, int synch)
> >  {
> >  	pgd_t *pgd;
> >  	pud_t *pud;
> > @@ -249,7 +253,7 @@ pte_t *page_check_address(struct page *p
> >
> >  	pte = pte_offset_map(pmd, address);
> >  	/* Make a quick check before getting the lock */
> > -	if (!pte_present(*pte)) {
> > +	if (!synch && !pte_present(*pte)) {
> >  		pte_unmap(pte);
> >  		return NULL;
> >  	}
> > @@ -281,7 +285,7 @@ static int page_referenced_one(struct pa
> >  	if (address == -EFAULT)
> >  		goto out;
> >
> > -	pte = page_check_address(page, mm, address, &ptl);
> > +	pte = page_check_address(page, mm, address, &ptl, 0);
> >  	if (!pte)
> >  		goto out;
> >
> > @@ -450,7 +454,7 @@ static int page_mkclean_one(struct page
> >  	if (address == -EFAULT)
> >  		goto out;
> >
> > -	pte = page_check_address(page, mm, address, &ptl);
> > +	pte = page_check_address(page, mm, address, &ptl, 1);
> >  	if (!pte)
> >  		goto out;
> >
> > @@ -697,7 +701,7 @@ static int try_to_unmap_one(struct page
> >  	if (address == -EFAULT)
> >  		goto out;
> >
> > -	pte = page_check_address(page, mm, address, &ptl);
> > +	pte = page_check_address(page, mm, address, &ptl, 0);
> >  	if (!pte)
> >  		goto out;
>
> --
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