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

Richard Kennedy · Ingo Molnar · commit af6a25f0e1ec · 2011-05-25T16:16:41.000+02:00
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 <richard@rsk.demon.co.uk> Cc: wilsons@start.ca Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Pekka Enberg <penberg@kernel.org> Link: http://lkml.kernel.org/r/1306244999.1999.5.camel@castor.rsk Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
@@ -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
