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Date: Thu, 2 Jun 2016 12:47:57 -0700 (PDT)
From: Hugh Dickins <hughd@google.com>
Subject: Re: [BUG/REGRESSION] THP: broken page count after commit aa88b68c
In-Reply-To: <20160602155149.GB8493@node.shutemov.name>
Message-ID: <alpine.LSU.2.11.1606021240310.10558@eggly.anvils>
References: <20160602172141.75c006a9@thinkpad> <20160602155149.GB8493@node.shutemov.name>
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Sender: owner-linux-mm@kvack.org
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To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Andrea Arcangeli <aarcange@redhat.com>, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>, Mel Gorman <mgorman@techsingularity.net>, Hugh Dickins <hughd@google.com>, Johannes Weiner <hannes@cmpxchg.org>, Dave Hansen <dave.hansen@intel.com>, Vlastimil Babka <vbabka@suse.cz>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christian Borntraeger <borntraeger@de.ibm.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>

On Thu, 2 Jun 2016, Kirill A. Shutemov wrote:
> On Thu, Jun 02, 2016 at 05:21:41PM +0200, Gerald Schaefer wrote:
> > 
> > The following quick hack fixed the issue:
> > 
> > diff --git a/mm/swap_state.c b/mm/swap_state.c
> > index 0d457e7..c99463a 100644
> > --- a/mm/swap_state.c
> > +++ b/mm/swap_state.c
> > @@ -252,7 +252,10 @@ static inline void free_swap_cache(struct page *page)
> >  void free_page_and_swap_cache(struct page *page)
> >  {
> >  	free_swap_cache(page);
> > -	put_page(page);
> > +	if (is_huge_zero_page(page))
> > +		put_huge_zero_page();
> > +	else
> > +		put_page(page);
> >  }
> >  
> >  /*
> 
> The fix looks good to me.

Is there a good reason why the refcount of the huge_zero_page is
huge_zero_refcount, instead of the refcount of the huge_zero_page?
Wouldn't the latter avoid such is_huge_zero_page() special-casing?

Hugh

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