linux-kernel - Re: [PATCH 4/4] mm: prepare page_referenced() and page

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Message-Id: <20151105163211.608eec970de21a95faf6e156@linux-foundation.org>
Date:	Thu, 5 Nov 2015 16:32:11 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Minchan Kim <minchan@...nel.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Vladimir Davydov <vdavydov@...allels.com>
Subject: Re: [PATCH 4/4] mm: prepare page_referenced() and page_idle to new
 THP refcounting

On Tue,  3 Nov 2015 17:26:15 +0200 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> wrote:

> I've missed two simlar codepath which need some preparation to work well
> with reworked THP refcounting.
> 
> Both page_referenced() and page_idle_clear_pte_refs_one() assume that
> THP can only be mapped with PMD, so there's no reason to look on PTEs
> for PageTransHuge() pages. That's no true anymore: THP can be mapped
> with PTEs too.
> 
> The patch removes PageTransHuge() test from the functions and opencode
> page table check.

x86_64 allnoconfig:

In file included from mm/rmap.c:47:
include/linux/mm.h: In function 'page_referenced':
include/linux/mm.h:448: error: call to '__compiletime_assert_448' declared with attribute error: BUILD_BUG failed
make[1]: *** [mm/rmap.o] Error 1
make: *** [mm/rmap.o] Error 2

because

#else /* CONFIG_TRANSPARENT_HUGEPAGE */
#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })


btw, total_mapcount() is far too large to be inlined and
page_mapcount() is getting pretty bad too.

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