Date: Thu, 3 Oct 2013 16:11:09 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Alex Thorlton <athorlton@sgi.com>, Ingo Molnar <mingo@redhat.com>,
        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>, Peter Zijlstra <peterz@infradead.org>,
        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: [PATCHv4 09/10] mm: implement split page table lock for PMD
 level
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On Fri, 27 Sep 2013 16:16:26 +0300 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote:

> The basic idea is the same as with PTE level: the lock is embedded into
> struct page of table's page.
> 
> We can't use mm->pmd_huge_pte to store pgtables for THP, since we don't
> take mm->page_table_lock anymore. Let's reuse page->lru of table's page
> for that.
> 
> pgtable_pmd_page_ctor() returns true, if initialization is successful
> and false otherwise. Current implementation never fails, but assumption
> that constructor can fail will help to port it to -rt where spinlock_t
> is rather huge and cannot be embedded into struct page -- dynamic
> allocation is required.

spinlock_t is rather large when lockdep is enabled.  What happens?
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