From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Andi Kleen <andi@firstfloor.org>,
        Michal Hocko <mhocko@suse.cz>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Rik van Riel <riel@redhat.com>, Andrea Arcangeli <aarcange@redhat.com>,
        kirill.shutemov@linux.intel.com,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Alex Thorlton <athorlton@sgi.com>, linux-kernel@vger.kernel.org
In-Reply-To: <1377883120-5280-3-git-send-email-n-horiguchi@ah.jp.nec.com>
References: <1377883120-5280-1-git-send-email-n-horiguchi@ah.jp.nec.com>
 <1377883120-5280-3-git-send-email-n-horiguchi@ah.jp.nec.com>
Subject: RE: [PATCH 2/2] thp: support split page table lock
Content-Transfer-Encoding: 7bit
Message-Id: <20130902105327.AE4D4E0090@blue.fi.intel.com>
Date: Mon,  2 Sep 2013 13:53:27 +0300 (EEST)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 876
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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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