Date: Thu, 5 Nov 2015 16:32:11 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Hugh Dickins <hughd@google.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Sasha Levin <sasha.levin@oracle.com>, Minchan Kim <minchan@kernel.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Vladimir Davydov <vdavydov@parallels.com>
Subject: Re: [PATCH 4/4] mm: prepare page_referenced() and page_idle to new
 THP refcounting
Message-Id: <20151105163211.608eec970de21a95faf6e156@linux-foundation.org>
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	<1446564375-72143-5-git-send-email-kirill.shutemov@linux.intel.com>
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On Tue,  3 Nov 2015 17:26:15 +0200 "Kirill A. Shutemov" <kirill.shutemov@linux.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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