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mm: pack compound_dtor and compound_order into one word in struct page

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The patch halves space occupied by compound_dtor and compound_order in
struct page.

For compound_order, it's trivial long -> short conversion.

For get_compound_page_dtor(), we now use hardcoded table for destructor
lookup and store its index in the struct page instead of direct pointer
to destructor. It shouldn't be a big trouble to maintain the table: we
have only two destructor and NULL currently.

This patch free up one word in tail pages for reuse. This is preparation
for the next patch.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov
2015-11-06 16:29:50 -08:00
committed by Linus Torvalds
parent 32e7ba1ea1
commit f1e61557f0
4 changed files with 35 additions and 14 deletions
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24
include/linux/mm.h
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@@ -568,18 +568,32 @@ int split_free_page(struct page *page);
/*
* Compound pages have a destructor function. Provide a
* prototype for that function and accessor functions.
* These are _only_ valid on the head of a PG_compound page.
* These are _only_ valid on the head of a compound page.
*/
typedef void compound_page_dtor(struct page *);
/* Keep the enum in sync with compound_page_dtors array in mm/page_alloc.c */
enum compound_dtor_id {
NULL_COMPOUND_DTOR,
COMPOUND_PAGE_DTOR,
#ifdef CONFIG_HUGETLB_PAGE
HUGETLB_PAGE_DTOR,
#endif
NR_COMPOUND_DTORS,
};
extern compound_page_dtor * const compound_page_dtors[];
static inline void set_compound_page_dtor(struct page *page,
compound_page_dtor *dtor)
enum compound_dtor_id compound_dtor)
{
page[1].compound_dtor = dtor;
VM_BUG_ON_PAGE(compound_dtor >= NR_COMPOUND_DTORS, page);
page[1].compound_dtor = compound_dtor;
}
static inline compound_page_dtor *get_compound_page_dtor(struct page *page)
{
return page[1].compound_dtor;
VM_BUG_ON_PAGE(page[1].compound_dtor >= NR_COMPOUND_DTORS, page);
return compound_page_dtors[page[1].compound_dtor];
}
static inline int compound_order(struct page *page)
@@ -589,7 +603,7 @@ static inline int compound_order(struct page *page)
return page[1].compound_order;
}
static inline void set_compound_order(struct page *page, unsigned long order)
static inline void set_compound_order(struct page *page, unsigned int order)
{
page[1].compound_order = order;
}