linux-kernel - RE: [PATCH 2/2] thp: support split page table lock

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Message-Id: <20130902105327.AE4D4E0090@blue.fi.intel.com>
Date:	Mon,  2 Sep 2013 13:53:27 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Andi Kleen <andi@...stfloor.org>,
	Michal Hocko <mhocko@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	kirill.shutemov@...ux.intel.com,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Alex Thorlton <athorlton@....com>, linux-kernel@...r.kernel.org
Subject: RE: [PATCH 2/2] thp: support split page table lock

Naoya Horiguchi wrote:
> Thp related code also uses per process mm->page_table_lock now. So making
> it fine-grained can provide better performance.
> 
> This patch makes thp support split page table lock which makes us use
> page->ptl of the pages storing "pmd_trans_huge" pmds.

Hm. So, you use page->ptl only when you deal with thp pages, otherwise
mm->page_table_lock, right?

It looks inconsistent to me. Does it mean we have to take both locks on
split and collapse paths? I'm not sure if it's safe to take only
page->ptl for alloc path. Probably not.

Why not to use new locking for pmd everywhere?

-- 
 Kirill A. Shutemov
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