Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=d85f33855c303acfa87fa457157cef755b6087df
Commit:     d85f33855c303acfa87fa457157cef755b6087df
Parent:     30520864839dc796fd314812e7036e754880b47d
Author:     Christoph Lameter <[EMAIL PROTECTED]>
AuthorDate: Sun May 6 14:49:39 2007 -0700
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Mon May 7 12:12:53 2007 -0700

    Make page->private usable in compound pages
    
    If we add a new flag so that we can distinguish between the first page and 
the
    tail pages then we can avoid to use page->private in the first page.
    page->private == page for the first page, so there is no real information in
    there.
    
    Freeing up page->private makes the use of compound pages more transparent.
    They become more usable like real pages.  Right now we have to be careful 
f.e.
     if we are going beyond PAGE_SIZE allocations in the slab on i386 because we
    can then no longer use the private field.  This is one of the issues that
    cause us not to support debugging for page size slabs in SLAB.
    
    Having page->private available for SLUB would allow more meta information in
    the page struct.  I can probably avoid the 16 bit ints that I have in there
    right now.
    
    Also if page->private is available then a compound page may be equipped with
    buffer heads.  This may free up the way for filesystems to support larger
    blocks than page size.
    
    We add PageTail as an alias of PageReclaim.  Compound pages cannot currently
    be reclaimed.  Because of the alias one needs to check PageCompound first.
    
    The RFC for the this approach was discussed at
    http://marc.info/?t=117574302800001&r=1&w=2
    
    [EMAIL PROTECTED]: fix hugetlbfs]
    Signed-off-by: Christoph Lameter <[EMAIL PROTECTED]>
    Signed-off-by: Nishanth Aravamudan <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 arch/ia64/mm/init.c        |    2 +-
 fs/hugetlbfs/inode.c       |    2 +-
 include/linux/mm.h         |   33 ++++++++++++++++++++++++++++-----
 include/linux/page-flags.h |   14 ++++++++++++++
 mm/internal.h              |    2 +-
 mm/page_alloc.c            |   29 ++++++++++++++++++++---------
 mm/slab.c                  |    6 ++----
 mm/slub.c                  |   19 ++++---------------
 mm/swap.c                  |    2 +-
 9 files changed, 72 insertions(+), 37 deletions(-)

diff --git a/arch/ia64/mm/init.c b/arch/ia64/mm/init.c
index 4f36987..2da8411 100644
--- a/arch/ia64/mm/init.c
+++ b/arch/ia64/mm/init.c
@@ -121,7 +121,7 @@ lazy_mmu_prot_update (pte_t pte)
                return;                         /* i-cache is already coherent 
with d-cache */
 
        if (PageCompound(page)) {
-               order = (unsigned long) (page[1].lru.prev);
+               order = compound_order(page);
                flush_icache_range(addr, addr + (1UL << order << PAGE_SHIFT));
        }
        else
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 9ba71b2..8e1b782 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -450,7 +450,7 @@ static int hugetlbfs_symlink(struct inode *dir,
  */
 static int hugetlbfs_set_page_dirty(struct page *page)
 {
-       struct page *head = (struct page *)page_private(page);
+       struct page *head = compound_head(page);
 
        SetPageDirty(head);
        return 0;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c95d96e..8c149fa 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -267,17 +267,28 @@ static inline int get_page_unless_zero(struct page *page)
        return atomic_inc_not_zero(&page->_count);
 }
 
+static inline struct page *compound_head(struct page *page)
+{
+       /*
+        * We could avoid the PageCompound(page) check if
+        * we would not overload PageTail().
+        *
+        * This check has to be done in several performance critical
+        * paths of the slab etc. IMHO PageTail deserves its own flag.
+        */
+       if (unlikely(PageCompound(page) && PageTail(page)))
+               return page->first_page;
+       return page;
+}
+
 static inline int page_count(struct page *page)
 {
-       if (unlikely(PageCompound(page)))
-               page = (struct page *)page_private(page);
-       return atomic_read(&page->_count);
+       return atomic_read(&compound_head(page)->_count);
 }
 
 static inline void get_page(struct page *page)
 {
-       if (unlikely(PageCompound(page)))
-               page = (struct page *)page_private(page);
+       page = compound_head(page);
        VM_BUG_ON(atomic_read(&page->_count) == 0);
        atomic_inc(&page->_count);
 }
@@ -314,6 +325,18 @@ static inline compound_page_dtor 
*get_compound_page_dtor(struct page *page)
        return (compound_page_dtor *)page[1].lru.next;
 }
 
+static inline int compound_order(struct page *page)
+{
+       if (!PageCompound(page) || PageTail(page))
+               return 0;
+       return (unsigned long)page[1].lru.prev;
+}
+
+static inline void set_compound_order(struct page *page, unsigned long order)
+{
+       page[1].lru.prev = (void *)order;
+}
+
 /*
  * Multiple processes may "see" the same page. E.g. for untouched
  * mappings of /dev/null, all processes see the same page full of
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 9632659..a1e1436 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -94,6 +94,12 @@
 /* PG_owner_priv_1 users should have descriptive aliases */
 #define PG_checked             PG_owner_priv_1 /* Used by some filesystems */
 
+/*
+ * Marks tail portion of a compound page. We currently do not reclaim
+ * compound pages so we can reuse a flag only used for reclaim here.
+ */
+#define PG_tail                        PG_reclaim
+
 #if (BITS_PER_LONG > 32)
 /*
  * 64-bit-only flags build down from bit 31
@@ -241,6 +247,14 @@ static inline void SetPageUptodate(struct page *page)
 #define __SetPageCompound(page)        __set_bit(PG_compound, &(page)->flags)
 #define __ClearPageCompound(page) __clear_bit(PG_compound, &(page)->flags)
 
+/*
+ * Note: PG_tail is an alias of another page flag. The result of PageTail()
+ * is only valid if PageCompound(page) is true.
+ */
+#define PageTail(page) test_bit(PG_tail, &(page)->flags)
+#define __SetPageTail(page)    __set_bit(PG_tail, &(page)->flags)
+#define __ClearPageTail(page)  __clear_bit(PG_tail, &(page)->flags)
+
 #ifdef CONFIG_SWAP
 #define PageSwapCache(page)    test_bit(PG_swapcache, &(page)->flags)
 #define SetPageSwapCache(page) set_bit(PG_swapcache, &(page)->flags)
diff --git a/mm/internal.h b/mm/internal.h
index d527b80..a3110c0 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -24,7 +24,7 @@ static inline void set_page_count(struct page *page, int v)
  */
 static inline void set_page_refcounted(struct page *page)
 {
-       VM_BUG_ON(PageCompound(page) && page_private(page) != (unsigned 
long)page);
+       VM_BUG_ON(PageCompound(page) && PageTail(page));
        VM_BUG_ON(atomic_read(&page->_count));
        set_page_count(page, 1);
 }
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 542fc08..fc241fe 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -225,7 +225,7 @@ static void bad_page(struct page *page)
 
 static void free_compound_page(struct page *page)
 {
-       __free_pages_ok(page, (unsigned long)page[1].lru.prev);
+       __free_pages_ok(page, compound_order(page));
 }
 
 static void prep_compound_page(struct page *page, unsigned long order)
@@ -234,12 +234,14 @@ static void prep_compound_page(struct page *page, 
unsigned long order)
        int nr_pages = 1 << order;
 
        set_compound_page_dtor(page, free_compound_page);
-       page[1].lru.prev = (void *)order;
-       for (i = 0; i < nr_pages; i++) {
+       set_compound_order(page, order);
+       __SetPageCompound(page);
+       for (i = 1; i < nr_pages; i++) {
                struct page *p = page + i;
 
+               __SetPageTail(p);
                __SetPageCompound(p);
-               set_page_private(p, (unsigned long)page);
+               p->first_page = page;
        }
 }
 
@@ -248,15 +250,19 @@ static void destroy_compound_page(struct page *page, 
unsigned long order)
        int i;
        int nr_pages = 1 << order;
 
-       if (unlikely((unsigned long)page[1].lru.prev != order))
+       if (unlikely(compound_order(page) != order))
                bad_page(page);
 
-       for (i = 0; i < nr_pages; i++) {
+       if (unlikely(!PageCompound(page)))
+                       bad_page(page);
+       __ClearPageCompound(page);
+       for (i = 1; i < nr_pages; i++) {
                struct page *p = page + i;
 
-               if (unlikely(!PageCompound(p) |
-                               (page_private(p) != (unsigned long)page)))
+               if (unlikely(!PageCompound(p) | !PageTail(p) |
+                               (p->first_page != page)))
                        bad_page(page);
+               __ClearPageTail(p);
                __ClearPageCompound(p);
        }
 }
@@ -429,13 +435,18 @@ static inline int free_pages_check(struct page *page)
                        1 << PG_private |
                        1 << PG_locked  |
                        1 << PG_active  |
-                       1 << PG_reclaim |
                        1 << PG_slab    |
                        1 << PG_swapcache |
                        1 << PG_writeback |
                        1 << PG_reserved |
                        1 << PG_buddy ))))
                bad_page(page);
+       /*
+        * PageReclaim == PageTail. It is only an error
+        * for PageReclaim to be set if PageCompound is clear.
+        */
+       if (unlikely(!PageCompound(page) && PageReclaim(page)))
+               bad_page(page);
        if (PageDirty(page))
                __ClearPageDirty(page);
        /*
diff --git a/mm/slab.c b/mm/slab.c
index 9cd01fa..f4b2e22 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -602,8 +602,7 @@ static inline void page_set_cache(struct page *page, struct 
kmem_cache *cache)
 
 static inline struct kmem_cache *page_get_cache(struct page *page)
 {
-       if (unlikely(PageCompound(page)))
-               page = (struct page *)page_private(page);
+       page = compound_head(page);
        BUG_ON(!PageSlab(page));
        return (struct kmem_cache *)page->lru.next;
 }
@@ -615,8 +614,7 @@ static inline void page_set_slab(struct page *page, struct 
slab *slab)
 
 static inline struct slab *page_get_slab(struct page *page)
 {
-       if (unlikely(PageCompound(page)))
-               page = (struct page *)page_private(page);
+       page = compound_head(page);
        BUG_ON(!PageSlab(page));
        return (struct slab *)page->lru.prev;
 }
diff --git a/mm/slub.c b/mm/slub.c
index 9d52cce..8fa1c6e 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1325,9 +1325,7 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
 
        page = virt_to_page(x);
 
-       if (unlikely(PageCompound(page)))
-               page = page->first_page;
-
+       page = compound_head(page);
 
        if (unlikely(PageError(page) && (s->flags & SLAB_STORE_USER)))
                set_tracking(s, x, TRACK_FREE);
@@ -1338,10 +1336,7 @@ EXPORT_SYMBOL(kmem_cache_free);
 /* Figure out on which slab object the object resides */
 static struct page *get_object_page(const void *x)
 {
-       struct page *page = virt_to_page(x);
-
-       if (unlikely(PageCompound(page)))
-               page = page->first_page;
+       struct page *page = compound_head(virt_to_page(x));
 
        if (!PageSlab(page))
                return NULL;
@@ -2081,10 +2076,7 @@ void kfree(const void *x)
        if (!x)
                return;
 
-       page = virt_to_page(x);
-
-       if (unlikely(PageCompound(page)))
-               page = page->first_page;
+       page = compound_head(virt_to_page(x));
 
        s = page->slab;
 
@@ -2120,10 +2112,7 @@ void *krealloc(const void *p, size_t new_size, gfp_t 
flags)
                return NULL;
        }
 
-       page = virt_to_page(p);
-
-       if (unlikely(PageCompound(page)))
-               page = page->first_page;
+       page = compound_head(virt_to_page(p));
 
        new_cache = get_slab(new_size, flags);
 
diff --git a/mm/swap.c b/mm/swap.c
index 2ed7be3..218c52a 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -55,7 +55,7 @@ static void fastcall __page_cache_release(struct page *page)
 
 static void put_compound_page(struct page *page)
 {
-       page = (struct page *)page_private(page);
+       page = compound_head(page);
        if (put_page_testzero(page)) {
                compound_page_dtor *dtor;
 
-
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