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x86: reorder mm_context_t to remove x86_64 alignment padding & so shrink mm_struct

PATCH In review Richard Kennedy 1 participant 2 messages May 24, 2011 – May 25, 2011 x86

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Richard Kennedy

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#0 lore raw

PATCH 1/1 x86: reorder mm_context_t to remove x86_64 alignment padding & so shrink mm_struct

Reorder mm_context_t to remove alignment padding on 64 bit builds shrinking its size from 64 to 56 bytes.

This allows mm_struct to shrink from 840 to 832 bytes, so using one fewer cache lines, and getting more objects per slab when using slub.

slabinfo mm_struct reports
before :-

Sizes (bytes) Slabs
-----------------------------------
Object : 840 Total : 7
SlabObj: 896 Full : 1
SlabSiz: 16384 Partial: 4
Loss : 56 CpuSlab: 2
Align : 64 Objects: 18

after :-

Sizes (bytes) Slabs
----------------------------------
Object : 832 Total : 7
SlabObj: 832 Full : 1
SlabSiz: 16384 Partial: 4
Loss : 0 CpuSlab: 2
Align : 64 Objects: 19

Signed-off-by Richard Kennedy <[email protected]>

---
patch against v2.6.39
compiled & tested on x86_64.

regards
Richard

arch/x86/include/asm/mmu.h +2 -2
index aeff3e8..5f55e69 100644
@@ -11,14 +11,14 @@
 typedef struct {
 	void *ldt;
 	int size;
-	struct mutex lock;
-	void *vdso;
 
 #ifdef CONFIG_X86_64
 	/* True if mm supports a task running in 32 bit compatibility mode. */
 	unsigned short ia32_compat;
 #endif
 
+	struct mutex lock;
+	void *vdso;
 } mm_context_t;
 
 #ifdef CONFIG_SMP
author
#1 lore raw

[tip:x86/urgent] x86: Reorder mm_context_t to remove x86_64 alignment padding and thus shrink mm_struct

Commit-ID:  af6a25f0e1ec0265c267e6ee4513925eaba6d0ed
Gitweb:     http://git.kernel.org/tip/af6a25f0e1ec0265c267e6ee4513925eaba6d0ed
Author:     Richard Kennedy <[email protected]>
AuthorDate: Tue, 24 May 2011 14:49:59 +0100
Committer:  Ingo Molnar <[email protected]>
CommitDate: Wed, 25 May 2011 16:16:41 +0200

x86: Reorder mm_context_t to remove x86_64 alignment padding and thus shrink mm_struct

Reorder mm_context_t to remove alignment padding on 64 bit builds shrinking its size from 64 to 56 bytes.

This allows mm_struct to shrink from 840 to 832 bytes, so using one fewer cache lines, and getting more objects per slab when using slub.

slabinfo mm_struct reports
before :-

Sizes (bytes) Slabs
-----------------------------------
Object : 840 Total : 7
SlabObj: 896 Full : 1
SlabSiz: 16384 Partial: 4
Loss : 56 CpuSlab: 2
Align : 64 Objects: 18

after :-

Sizes (bytes) Slabs
----------------------------------
Object : 832 Total : 7
SlabObj: 832 Full : 1
SlabSiz: 16384 Partial: 4
Loss : 0 CpuSlab: 2
Align : 64 Objects: 19

Signed-off-by Richard Kennedy <[email protected]>
Cc [email protected]
Cc Linus Torvalds <[email protected]>
Cc Andrew Morton <[email protected]>
Cc Pekka Enberg <[email protected]>
Link http://lkml.kernel.org/r/[email protected] open here
Signed-off-by Ingo Molnar <[email protected]>
---
 arch/x86/include/asm/mmu.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
arch/x86/include/asm/mmu.h +2 -2
index aeff3e8..5f55e69 100644
@@ -11,14 +11,14 @@
 typedef struct {
 	void *ldt;
 	int size;
-	struct mutex lock;
-	void *vdso;
 
 #ifdef CONFIG_X86_64
 	/* True if mm supports a task running in 32 bit compatibility mode. */
 	unsigned short ia32_compat;
 #endif
 
+	struct mutex lock;
+	void *vdso;
 } mm_context_t;
 
 #ifdef CONFIG_SMP