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

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>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 906c46a0570712d88481efb5ef9d077836124707..6581c21320cbb67819a057553c50aec969c8a962 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -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;
 }

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index c0ec46df6c1349f63af65f21da0f946c484dbad2..e334ef79cb436dda88dc7bc409a60d28430744e2 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -28,8 +28,6 @@ struct mem_cgroup;
                IS_ENABLED(CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK))
 #define ALLOC_SPLIT_PTLOCKS    (SPINLOCK_SIZE > BITS_PER_LONG/8)
 
-typedef void compound_page_dtor(struct page *);
-
 /*
  * Each physical page in the system has a struct page associated with
  * it to keep track of whatever it is we are using the page for at the
@@ -136,8 +134,8 @@ struct page {
                                                 */
                /* First tail page of compound page */
                struct {
-                       compound_page_dtor *compound_dtor;
-                       unsigned long compound_order;
+                       unsigned short int compound_dtor;
+                       unsigned short int compound_order;
                };
 
 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 089cccfa8b02421c8e7c33ad0dd5bf8e3f6ebbba..6832707c336a3917e279593aa29d6119403f7038 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1146,7 +1146,7 @@ static void update_and_free_page(struct hstate *h, struct page *page)
                                1 << PG_writeback);
        }
        VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
-       set_compound_page_dtor(page, NULL);
+       set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
        set_page_refcounted(page);
        if (hstate_is_gigantic(h)) {
                destroy_compound_gigantic_page(page, huge_page_order(h));
@@ -1242,7 +1242,7 @@ void free_huge_page(struct page *page)
 static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
 {
        INIT_LIST_HEAD(&page->lru);
-       set_compound_page_dtor(page, free_huge_page);
+       set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
        spin_lock(&hugetlb_lock);
        set_hugetlb_cgroup(page, NULL);
        h->nr_huge_pages++;
@@ -1294,7 +1294,7 @@ int PageHuge(struct page *page)
                return 0;
 
        page = compound_head(page);
-       return get_compound_page_dtor(page) == free_huge_page;
+       return page[1].compound_dtor == HUGETLB_PAGE_DTOR;
 }
 EXPORT_SYMBOL_GPL(PageHuge);
 
@@ -1563,7 +1563,7 @@ static struct page *__alloc_buddy_huge_page(struct hstate *h,
        if (page) {
                INIT_LIST_HEAD(&page->lru);
                r_nid = page_to_nid(page);
-               set_compound_page_dtor(page, free_huge_page);
+               set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
                set_hugetlb_cgroup(page, NULL);
                /*
                 * We incremented the global counters already

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b69e31586eaaf1f210065792e7526d1aac488ab9..441f2b2bb5b2a81b3a818639fc454c4454fbf8f6 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -229,6 +229,15 @@ static char * const zone_names[MAX_NR_ZONES] = {
 #endif
 };
 
+static void free_compound_page(struct page *page);
+compound_page_dtor * const compound_page_dtors[] = {
+       NULL,
+       free_compound_page,
+#ifdef CONFIG_HUGETLB_PAGE
+       free_huge_page,
+#endif
+};
+
 int min_free_kbytes = 1024;
 int user_min_free_kbytes = -1;
 
@@ -458,7 +467,7 @@ void prep_compound_page(struct page *page, unsigned long order)
        int i;
        int nr_pages = 1 << order;
 
-       set_compound_page_dtor(page, free_compound_page);
+       set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
        set_compound_order(page, order);
        __SetPageHead(page);
        for (i = 1; i < nr_pages; i++) {