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

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Message-ID: <5555A3D1.3010108@suse.cz>
Date:	Fri, 15 May 2015 09:44:17 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
CC:	Dave Hansen <dave.hansen@...el.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 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> As with rmap, with new refcounting we cannot rely on PageTransHuge() to
> check if we need to charge size of huge page form the cgroup. We need to
> get information from caller to know whether it was mapped with PMD or
> PTE.
>
> We do uncharge when last reference on the page gone. At that point if we
> see PageTransHuge() it means we need to unchange whole huge page.
>
> The tricky part is partial unmap -- when we try to unmap part of huge
> page. We don't do a special handing of this situation, meaning we don't
> uncharge the part of huge page unless last user is gone or
> split_huge_page() is triggered. In case of cgroup memory pressure
> happens the partial unmapped page will be split through shrinker. This
> should be good enough.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@...cle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

But same question about whether it should be using hpage_nr_pages() 
instead of a constant.

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