mm: mm_struct: remove 16 bytes of alignment padding on 64 bit builds

Reorder mm_struct to remove 16 bytes of alignment padding on 64 bit
builds.  On my config this shrinks mm_struct by enough to fit in one
fewer cache lines and allows more objects per slab in mm_struct
kmem_cache under SLUB.

slabinfo before patch :-
    Sizes (bytes)     Slabs
    --------------------------------
    Object :     848  Total  :       9
    SlabObj:     896  Full   :       2
    SlabSiz:   16384  Partial:       5
    Loss   :      48  CpuSlab:       2
    Align  :      64  Objects:      18

 slabinfo after :-
    Sizes (bytes)     Slabs
    --------------------------------
    Object :     832  Total  :       7
    SlabObj:     832  Full   :       2
    SlabSiz:   16384  Partial:       3
    Loss   :       0  CpuSlab:       2
    Align  :      64  Objects:      19

Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 26bc4e2cd2750aea3695f9f38a8e365716f764ac..02aa5619709b9bab0a40d183fc3b0b017b8bd50c 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -237,8 +237,9 @@ struct mm_struct {
        atomic_t mm_users;                      /* How many users with user space? */
        atomic_t mm_count;                      /* How many references to "struct mm_struct" (users count as 1) */
        int map_count;                          /* number of VMAs */
-       struct rw_semaphore mmap_sem;
+
        spinlock_t page_table_lock;             /* Protects page tables and some counters */
+       struct rw_semaphore mmap_sem;
 
        struct list_head mmlist;                /* List of maybe swapped mm's.  These are globally strung
                                                 * together off init_mm.mmlist, and are protected
@@ -281,6 +282,9 @@ struct mm_struct {
        unsigned int token_priority;
        unsigned int last_interval;
 
+       /* How many tasks sharing this mm are OOM_DISABLE */
+       atomic_t oom_disable_count;
+
        unsigned long flags; /* Must use atomic bitops to access the bits */
 
        struct core_state *core_state; /* coredumping support */
@@ -313,8 +317,6 @@ struct mm_struct {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
        pgtable_t pmd_huge_pte; /* protected by page_table_lock */
 #endif
-       /* How many tasks sharing this mm are OOM_DISABLE */
-       atomic_t oom_disable_count;
 };
 
 /* Future-safe accessor for struct mm_struct's cpu_vm_mask. */