Date: Fri, 13 Sep 2013 15:24:35 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Alex Thorlton <athorlton@sgi.com>, Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Al Viro <viro@zeniv.linux.org.uk>, Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Dave Hansen <dave.hansen@intel.com>, Dave Jones <davej@redhat.com>,
        David Howells <dhowells@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Kees Cook <keescook@chromium.org>, Mel Gorman <mgorman@suse.de>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Rik van Riel <riel@redhat.com>,
        Robin Holt <robinmholt@gmail.com>, Sedat Dilek <sedat.dilek@gmail.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH 8/9] mm: implement split page table lock for PMD level
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On Fri, Sep 13, 2013 at 04:06:15PM +0300, Kirill A. Shutemov wrote:
> The basic idea is the same as with PTE level: the lock is embedded into
> struct page of table's page.
> 
> Split pmd page table lock only makes sense on big machines.
> Let's say >= 32 CPUs for now.

Why is this? Couldn't I generate the same amount of contention on PMD
level as I can on PTE level in the THP case?


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