linux-kernel - [PATCHv5 01/11] mm: avoid increase sizeof(struct page) due to split page table lock

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Date:	Mon,  7 Oct 2013 16:54:03 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Alex Thorlton <athorlton@....com>, Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	"Eric W . Biederman" <ebiederm@...ssion.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Dave Jones <davej@...hat.com>,
	David Howells <dhowells@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Kees Cook <keescook@...omium.org>,
	Mel Gorman <mgorman@...e.de>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Robin Holt <robinmholt@...il.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv5 01/11] mm: avoid increase sizeof(struct page) due to split page table lock

CONFIG_GENERIC_LOCKBREAK increases sizeof(spinlock_t) to 8 bytes.
It leads to increase sizeof(struct page) by 4 bytes on 32-bit system if
split page table lock is in use, since page->ptl shares space in union
with longs and pointers.

Let's disable split page table lock on 32-bit systems with
GENERIC_LOCKBREAK enabled.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index 026771a9b0..6f5be0dac9 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -212,6 +212,7 @@ config SPLIT_PTLOCK_CPUS
 	default "999999" if ARM && !CPU_CACHE_VIPT
 	default "999999" if PARISC && !PA20
 	default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC
+	default "999999" if !64BIT && GENERIC_LOCKBREAK
 	default "4"
 
 #
-- 
1.8.4.rc3

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