linux-kernel - Re: [PATCH] HWPOISON: fix wrong num_poisoned

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Date:	Thu, 31 Jan 2013 18:35:45 -0500
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andi Kleen <andi@...stfloor.org>,
	Tony Luck <tony.luck@...el.com>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HWPOISON: fix wrong num_poisoned_pages in handling memory error on thp

On Thu, Jan 31, 2013 at 11:34:16AM -0800, Andrew Morton wrote:
> On Thu, 31 Jan 2013 10:25:58 -0500
> Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:
> 
> > num_poisoned_pages counts up the number of pages isolated by memory errors.
> > But for thp, only one subpage is isolated because memory error handler
> > splits it, so it's wrong to add (1 << compound_trans_order).
> > 
> > ...
> >
> > --- mmotm-2013-01-23-17-04.orig/mm/memory-failure.c
> > +++ mmotm-2013-01-23-17-04/mm/memory-failure.c
> > @@ -1039,7 +1039,14 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
> >  		return 0;
> >  	}
> >  
> > -	nr_pages = 1 << compound_trans_order(hpage);
> > +	/*
> > +	 * If a thp is hit by a memory failure, it's supposed to be split.
> > +	 * So we should add only one to num_poisoned_pages for that case.
> > +	 */
> > +	if (PageHuge(p))
> 
> /*
>  * PageHuge() only returns true for hugetlbfs pages, but not for normal or
>  * transparent huge pages.  See the PageTransHuge() documentation for more
>  * details.
>  */
> int PageHuge(struct page *page)
> {

Do you mean that my comment refers to thp but this if-condition uses
PageHuge so it's confusing, right?
And yes, that's right, so I want to change this comment like this:

   /*
    * Currently errors on hugetlbfs pages are contained in hugepage
    * unit, so nr_pages should be 1 << compound_order. OTOH when
    * errors are on transparent hugepages, they are supposed to be
    * split and error containment is done in normal page unit.
    * So nr_pages should be one in this case.
    */

> 
> > +		nr_pages = 1 << compound_trans_order(hpage);

I should've used compound_order because this code is run only for
hugetlbfs pages.

> > +	else /* normal page or thp */
> > +		nr_pages = 1;
> >  	atomic_long_add(nr_pages, &num_poisoned_pages);
> >  
> >  	/*

Thanks,
Naoya
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