linux-kernel - [PATCH -mm v2 02/11] mm: rearrange vm_area

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Date:	Thu, 21 Jun 2012 17:57:06 -0400
From:	Rik van Riel <riel@...riel.com>
To:	linux-mm@...ck.org
Cc:	akpm@...ux-foundation.org, aarcange@...hat.com,
	peterz@...radead.org, minchan@...il.com, kosaki.motohiro@...il.com,
	andi@...stfloor.org, hannes@...xchg.org, mel@....ul.ie,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...riel.com>,
	Rik van Riel <riel@...hat.com>
Subject: [PATCH -mm v2 02/11] mm: rearrange vm_area_struct for fewer cache misses

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: 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 9fc0291..23bd1e2 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -199,7 +199,8 @@ 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. */
@@ -207,9 +208,6 @@ 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;
 
 	/*
@@ -220,6 +218,12 @@ struct vm_area_struct {
 	 */
 	unsigned long free_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 prio tree, or
-- 
1.7.7.6

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