Date: Sun, 17 May 2015 02:17:32 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Hugh Dickins <hughd@google.com>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>, Christoph Lameter <cl@gentwo.org>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Steve Capper <steve.capper@linaro.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>,
        Jerome Marchand <jmarchan@redhat.com>,
        Sasha Levin <sasha.levin@oracle.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCHv5 03/28] memcg: adjust to support new THP refcounting
Message-ID: <20150516231732.GA13265@node.dhcp.inet.fi>
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On Fri, May 15, 2015 at 07:57:39AM -0700, Dave Hansen wrote:
> On 05/15/2015 04:18 AM, Kirill A. Shutemov wrote:
> >> > But same question about whether it should be using hpage_nr_pages() instead
> >> > of a constant.
> > No. Compiler woundn't be able to optimize HPAGE_PMD_NR away for THP=n,
> > since compound value cross compilation unit barrier.
> 
> What code are you talking about here, specifically?  This?
> 
> static inline int hpage_nr_pages(struct page *page)
> {
>         if (unlikely(PageTransHuge(page)))
>                 return HPAGE_PMD_NR;
>         return 1;
> }

No. See for instance mem_cgroup_try_charge(). Vlastimil would like to
replace hpage_nr_pages() call with plain HPAGE_PMD_NR.

-- 
 Kirill A. Shutemov
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