linux-kernel - Re: [PATCHv3, RFC 32/34] thp: handle write-protect exception to file-backed huge pages

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Date:	Fri, 26 Apr 2013 18:31:04 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Dave Hansen <dave@...1.net>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3, RFC 32/34] thp: handle write-protect exception to
 file-backed huge pages

Dave Hansen wrote:
> > +			if (!PageAnon(page)) {
> > +				add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
> > +				add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
> > +			}
> 
> This seems like a bit of a hack.  Shouldn't we have just been accounting
> to MM_FILEPAGES in the first place?

No, it's not.

It handles MAP_PRIVATE file mappings. The page was read first and
accounted to MM_FILEPAGES and then COW'ed by anon page here, so we have to
adjust counters. do_wp_page() has similar code.

-- 
 Kirill A. Shutemov
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