linux-kernel - Re: [PATCHv5 03/28] memcg: adjust to support new THP refcounting

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Date:	Fri, 15 May 2015 07:57:39 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Vlastimil Babka <vbabka@...e.cz>
CC:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv5 03/28] memcg: adjust to support new THP refcounting

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;
}

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