linux-kernel - [PATCH 04/16] mm: rearrange vm_area

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Message-Id: <1352155633-8648-5-git-send-email-walken@google.com>
Date:	Mon,  5 Nov 2012 14:47:01 -0800
From:	Michel Lespinasse <walken@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	"David S. Miller" <davem@...emloft.net>,
	Chris Metcalf <cmetcalf@...era.com>, x86@...nel.org,
	William Irwin <wli@...omorphy.com>
Cc:	linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
	linux-mips@...ux-mips.org, linux-sh@...r.kernel.org,
	sparclinux@...r.kernel.org, Rik van Riel <riel@...riel.com>
Subject: [PATCH 04/16] mm: rearrange vm_area_struct for fewer cache misses

From: Rik van Riel <riel@...riel.com>

The kernel walks the VMA rbtree in various places, including
the page fault path.  However, the vm_rb node spanned two
cache lines, on 64 bit systems with 64 byte cache lines (most
x86 systems).

Rearrange vm_area_struct a little, so all the information we
need to do a VMA tree walk is in the first cache line.

Signed-off-by: Michel Lespinasse <walken@...gle.com>
Signed-off-by: Rik van Riel <riel@...hat.com>

---
 include/linux/mm_types.h |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 94fa52b28ee8..528da4abf8ee 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -224,7 +224,8 @@ struct vm_region {
  * library, the executable area etc).
  */
 struct vm_area_struct {
-	struct mm_struct * vm_mm;	/* The address space we belong to. */
+	/* The first cache line has the info for VMA tree walking. */
+
 	unsigned long vm_start;		/* Our start address within vm_mm. */
 	unsigned long vm_end;		/* The first byte after our end address
 					   within vm_mm. */
@@ -232,9 +233,6 @@ struct vm_area_struct {
 	/* linked list of VM areas per task, sorted by address */
 	struct vm_area_struct *vm_next, *vm_prev;
 
-	pgprot_t vm_page_prot;		/* Access permissions of this VMA. */
-	unsigned long vm_flags;		/* Flags, see mm.h. */
-
 	struct rb_node vm_rb;
 
 	/*
@@ -245,6 +243,12 @@ struct vm_area_struct {
 	 */
 	unsigned long rb_subtree_gap;
 
+	/* Second cache line starts here. */
+
+	struct mm_struct * vm_mm;	/* The address space we belong to. */
+	pgprot_t vm_page_prot;		/* Access permissions of this VMA. */
+	unsigned long vm_flags;		/* Flags, see mm.h. */
+
 	/*
 	 * For areas with an address space and backing store,
 	 * linkage into the address_space->i_mmap interval tree, or
-- 
1.7.7.3
--
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