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

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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>
This commit is contained in:
Richard Kennedy 2011-05-24 14:49:59 +01:00 committed by Ingo Molnar
parent f073cc8f39
commit af6a25f0e1
1 changed files with 2 additions and 2 deletions
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4
arch/x86/include/asm/mmu.h
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@ -11,14 +11,14 @@
typedef struct { typedef struct {
void *ldt; void *ldt;
int size; int size;
struct mutex lock;
void *vdso;
#ifdef CONFIG_X86_64 #ifdef CONFIG_X86_64
/* True if mm supports a task running in 32 bit compatibility mode. */ /* True if mm supports a task running in 32 bit compatibility mode. */
unsigned short ia32_compat; unsigned short ia32_compat;
#endif #endif
struct mutex lock;
void *vdso;
} mm_context_t; } mm_context_t;
#ifdef CONFIG_SMP #ifdef CONFIG_SMP