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From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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Subject: Re: [PATCH 22/23] thp, mm: split huge page on mmap file page
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Message-Id: <20130809145006.95333E0090@blue.fi.intel.com>
Date: Fri,  9 Aug 2013 17:50:06 +0300 (EEST)
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To: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Andrea Arcangeli <aarcange@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Al Viro <viro@zeniv.linux.org.uk>, Hugh Dickins <hughd@google.com>, Wu Fengguang <fengguang.wu@intel.com>, Jan Kara <jack@suse.cz>, Mel Gorman <mgorman@suse.de>, linux-mm@kvack.org, Andi Kleen <ak@linux.intel.com>, Matthew Wilcox <willy@linux.intel.com>, "Kirill A. Shutemov" <kirill@shutemov.name>, Hillf Danton <dhillf@gmail.com>, Dave Hansen <dave@sr71.net>, Ning Qu <quning@google.com>, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org

Khalid Aziz wrote:
> On Sun, 2013-08-04 at 05:17 +0300, Kirill A. Shutemov wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > 
> > We are not ready to mmap file-backed tranparent huge pages. Let's split
> > them on fault attempt.
> > 
> > Later we'll implement mmap() properly and this code path be used for
> > fallback cases.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > ---
> >  mm/filemap.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index ed65af5..f7857ef 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -1743,6 +1743,8 @@ retry_find:
> >  			goto no_cached_page;
> >  	}
> >  
> > +	if (PageTransCompound(page))
> > +		split_huge_page(compound_trans_head(page));
> 
> Since PageTransCompound(page) returns true for transparent huge pages as
> well as hugetlbfs pages, could this code split hugetlbfs pages on an
> mmap() on to hugetlbfs pages? hugetlbfs pages are not supposed to be
> split, right?

hugetlbfs page cannot (should not) be here. hugetlb uses different
vm_ops->fault handeler.

-- 
 Kirill A. Shutemov

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