[PATCH] new struct page shrinkage

The patch has been changed like you wanted, with page->zone
shoved into page->flags. I've also pulled the thing up to
your latest changes from linux.bkbits.net so you should be
able to just pull it into your tree from:

Rik

drivers/char/agp/agpgart_be.c

@@ -830,7 +830,7 @@ static void agp_generic_destroy_page(unsigned long addr)
 	page = virt_to_page(pt);
 	atomic_dec(&page->count);
 	clear_bit(PG_locked, &page->flags);
-	wake_up(&page->wait);
+	wake_up_page(page);
 	free_page((unsigned long) pt);
 	atomic_dec(&agp_bridge.current_memory_agp);
 }
@@ -2828,7 +2828,7 @@ static void ali_destroy_page(unsigned long addr)
 	page = virt_to_page(pt);
 	atomic_dec(&page->count);
 	clear_bit(PG_locked, &page->flags);
-	wake_up(&page->wait);
+	wake_up_page(page);
 	free_page((unsigned long) pt);
 	atomic_dec(&agp_bridge.current_memory_agp);
 }

drivers/char/drm/i810_dma.c

@@ -294,14 +294,13 @@ static unsigned long i810_alloc_page(drm_device_t *dev)
 
 static void i810_free_page(drm_device_t *dev, unsigned long page)
 {
-	if(page == 0UL)
-		return;
-
-	atomic_dec(&virt_to_page(page)->count);
-	clear_bit(PG_locked, &virt_to_page(page)->flags);
-	wake_up(&virt_to_page(page)->wait);
-	free_page(page);
-	return;
+	if (page) {
+		struct page *p = virt_to_page(page);
+		atomic_dec(p);
+		clear_bit(PG_locked, &p->flags);
+		wake_up_page(p);
+		free_page(page);
+	}
 }
 
 static int i810_dma_cleanup(drm_device_t *dev)

fs/buffer.c

@@ -2115,8 +2115,7 @@ int generic_direct_IO(int rw, struct inode * inode, struct kiobuf * iobuf, unsig
  * of kiobuf structs (much like a user-space iovec list).
  *
  * The kiobuf must already be locked for IO.  IO is submitted
- * asynchronously: you need to check page->locked, page->uptodate, and
- * maybe wait on page->wait.
+ * asynchronously: you need to check page->locked and page->uptodate.
  *
  * It is up to the caller to make sure that there are enough blocks
  * passed in to completely map the iobufs to disk.
@@ -2173,8 +2172,8 @@ int brw_kiovec(int rw, int nr, struct kiobuf *iovec[], kdev_t dev, sector_t b[],
 /*
  * Start I/O on a page.
  * This function expects the page to be locked and may return
- * before I/O is complete. You then have to check page->locked,
- * page->uptodate, and maybe wait on page->wait.
+ * before I/O is complete. You then have to check page->locked
+ * and page->uptodate.
  *
  * brw_page() is SMP-safe, although it's being called with the
  * kernel lock held - but the code is ready.

include/asm-alpha/pgtable.h

@@ -268,8 +268,6 @@ extern inline int pgd_bad(pgd_t pgd)		{ return (pgd_val(pgd) & ~_PFN_MASK) != _P
 extern inline int pgd_present(pgd_t pgd)	{ return pgd_val(pgd) & _PAGE_VALID; }
 extern inline void pgd_clear(pgd_t * pgdp)	{ pgd_val(*pgdp) = 0; }
 
-#define page_address(page)	((page)->virtual)
-
 /*
  * The following only work if pte_present() is true.
  * Undefined behaviour if not..

include/asm-arm/pgtable.h

@@ -99,7 +99,6 @@ extern struct page *empty_zero_page;
 /*
  * Permanent address of a page. We never have highmem, so this is trivial.
  */
-#define page_address(page)	((page)->virtual)
 #define pages_to_mb(x)		((x) >> (20 - PAGE_SHIFT))
 
 /*

include/asm-cris/pgtable.h

@@ -439,7 +439,6 @@ static inline unsigned long __pte_page(pte_t pte)
 
 /* permanent address of a page */
 
-#define page_address(page)      ((page)->virtual)
 #define __page_address(page)    (PAGE_OFFSET + (((page) - mem_map) << PAGE_SHIFT))
 #define pte_page(pte)           (mem_map+pte_pagenr(pte))
 

include/asm-i386/pgtable.h

@@ -264,11 +264,7 @@ extern unsigned long pg0[1024];
 #define pmd_clear(xp)	do { set_pmd(xp, __pmd(0)); } while (0)
 #define	pmd_bad(x)	((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)
 
-/*
- * Permanent address of a page. Obviously must never be
- * called on a highmem page.
- */
-#define page_address(page) ((page)->virtual)
+
 #define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))
 
 /*

include/asm-ia64/pgtable.h

@@ -165,11 +165,6 @@
  * addresses:
  */
 
-/*
- * Given a pointer to an mem_map[] entry, return the kernel virtual
- * address corresponding to that page.
- */
-#define page_address(page)	((page)->virtual)
 
 /* Quick test to see if ADDR is a (potentially) valid physical address. */
 static inline long

include/asm-mips/pgtable.h

@@ -331,11 +331,6 @@ extern inline int pgd_bad(pgd_t pgd)		{ return 0; }
 extern inline int pgd_present(pgd_t pgd)	{ return 1; }
 extern inline void pgd_clear(pgd_t *pgdp)	{ }
 
-/*
- * Permanent address of a page.  On MIPS we never have highmem, so this
- * is simple.
- */
-#define page_address(page)	((page)->virtual)
 #ifdef CONFIG_CPU_VR41XX
 #define pte_page(x)             (mem_map+(unsigned long)((pte_val(x) >> (PAGE_SHIFT + 2))))
 #else

include/asm-mips64/pgtable.h

@@ -370,11 +370,6 @@ extern inline void pgd_clear(pgd_t *pgdp)
 	pgd_val(*pgdp) = ((unsigned long) invalid_pmd_table);
 }
 
-/*
- * Permanent address of a page.  On MIPS64 we never have highmem, so this
- * is simple.
- */
-#define page_address(page)	((page)->virtual)
 #ifndef CONFIG_DISCONTIGMEM
 #define pte_page(x)		(mem_map+(unsigned long)((pte_val(x) >> PAGE_SHIFT)))
 #else

include/asm-parisc/pgtable.h

@@ -275,7 +275,6 @@ extern inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
  * Permanent address of a page. Obviously must never be
  * called on a highmem page.
  */
-#define page_address(page) ({ if (!(page)->virtual) BUG(); (page)->virtual; })
 #define __page_address(page) ({ if (PageHighMem(page)) BUG(); PAGE_OFFSET + (((page) - mem_map) << PAGE_SHIFT); })
 #define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))
 #define pte_page(x) (mem_map+pte_pagenr(x))

include/asm-ppc/pgtable.h

@@ -389,10 +389,6 @@ extern unsigned long empty_zero_page[1024];
 #define	pmd_present(pmd)	((pmd_val(pmd) & PAGE_MASK) != 0)
 #define	pmd_clear(pmdp)		do { pmd_val(*(pmdp)) = 0; } while (0)
 
-/*
- * Permanent address of a page.
- */
-#define page_address(page)	((page)->virtual)
 #define pte_page(x)		(mem_map+(unsigned long)((pte_val(x)-PPC_MEMSTART) >> PAGE_SHIFT))
 
 #ifndef __ASSEMBLY__

include/asm-s390/pgtable.h

@@ -239,10 +239,6 @@ extern inline void set_pte(pte_t *pteptr, pte_t pteval)
 	*pteptr = pteval;
 }
 
-/*
- * Permanent address of a page.
- */
-#define page_address(page) ((page)->virtual)
 #define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))
 
 /*

include/asm-s390x/pgtable.h

@@ -234,10 +234,6 @@ extern inline void set_pte(pte_t *pteptr, pte_t pteval)
 	*pteptr = pteval;
 }
 
-/*
- * Permanent address of a page.
- */
-#define page_address(page) ((page)->virtual)
 #define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))
 
 /*

include/asm-sh/pgtable.h

@@ -208,11 +208,6 @@ extern unsigned long empty_zero_page[1024];
 #define pmd_clear(xp)	do { set_pmd(xp, __pmd(0)); } while (0)
 #define	pmd_bad(x)	((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)
 
-/*
- * Permanent address of a page. Obviously must never be
- * called on a highmem page.
- */
-#define page_address(page)  ((page)->virtual) /* P1 address of the page */
 #define pages_to_mb(x)	((x) >> (20-PAGE_SHIFT))
 #define pte_page(x) 	phys_to_page(pte_val(x)&PTE_PHYS_MASK)
 

include/asm-sparc/pgtable.h

@@ -293,9 +293,6 @@ BTFIXUPDEF_CALL_CONST(pte_t, pte_mkyoung, pte_t)
 #define page_pte_prot(page, prot)	mk_pte(page, prot)
 #define page_pte(page)			page_pte_prot(page, __pgprot(0))
 
-/* Permanent address of a page. */
-#define page_address(page)  ((page)->virtual)
-
 BTFIXUPDEF_CALL(struct page *, pte_page, pte_t)
 #define pte_page(pte) BTFIXUP_CALL(pte_page)(pte)
 

include/asm-sparc64/page.h

@@ -30,6 +30,9 @@ extern void do_BUG(const char *file, int line);
 
 #define PAGE_BUG(page)	BUG()
 
+/* Sparc64 is slow at multiplication, we prefer to use some extra space. */
+#define WANT_PAGE_VIRTUAL 1
+
 extern void _clear_page(void *page);
 #define clear_page(X)	_clear_page((void *)(X))
 extern void clear_user_page(void *page, unsigned long vaddr);

include/asm-sparc64/pgtable.h

@@ -243,8 +243,7 @@ extern inline pte_t pte_modify(pte_t orig_pte, pgprot_t new_prot)
 #define pte_mkold(pte)		(__pte(((pte_val(pte)<<1UL)>>1UL) & ~_PAGE_ACCESSED))
 
 /* Permanent address of a page. */
-#define __page_address(page)	((page)->virtual)
-#define page_address(page)	({ __page_address(page); })
+#define __page_address(page)	page_address(page)
 
 #define pte_page(x) (mem_map+(((pte_val(x)&_PAGE_PADDR)-phys_base)>>PAGE_SHIFT))
 

include/asm-x86_64/pgtable.h

@@ -289,7 +289,6 @@ extern void __handle_bad_pmd_kernel(pmd_t * pmd);
  * Permanent address of a page. Obviously must never be
  * called on a highmem page.
  */
-#define page_address(page) ((page)->virtual)
 #define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))	/* FIXME: is this
 						   right? */
 #define pte_page(x) (mem_map+((unsigned long)((pte_val(x) >> PAGE_SHIFT))))

include/linux/mm.h

@@ -157,12 +157,23 @@ typedef struct page {
 					   updated asynchronously */
 	struct list_head lru;		/* Pageout list, eg. active_list;
 					   protected by pagemap_lru_lock !! */
-	wait_queue_head_t wait;		/* Page locked?  Stand in line... */
 	struct page **pprev_hash;	/* Complement to *next_hash. */
 	struct buffer_head * buffers;	/* Buffer maps us to a disk block. */
+
+	/*
+	 * On machines where all RAM is mapped into kernel address space,
+	 * we can simply calculate the virtual address. On machines with
+	 * highmem some memory is mapped into kernel virtual memory
+	 * dynamically, so we need a place to store that address.
+	 * Note that this field could be 16 bits on x86 ... ;)
+	 *
+	 * Architectures with slow multiplication can define
+	 * WANT_PAGE_VIRTUAL in asm/page.h
+	 */
+#if defined(CONFIG_HIGHMEM) || defined(WANT_PAGE_VIRTUAL)
 	void *virtual;			/* Kernel virtual address (NULL if
 					   not kmapped, ie. highmem) */
-	struct zone_struct *zone;	/* Memory zone we are in. */
+#endif /* CONFIG_HIGMEM || WANT_PAGE_VIRTUAL */
 } mem_map_t;
 
 /*
@@ -183,6 +194,11 @@ typedef struct page {
 #define page_count(p)		atomic_read(&(p)->count)
 #define set_page_count(p,v) 	atomic_set(&(p)->count, v)
 
+static inline void init_page_count(struct page *page)
+{
+	page->count.counter = 0;
+}
+
 /*
  * Various page->flags bits:
  *
@@ -237,7 +253,7 @@ typedef struct page {
  * - private pages which have been modified may need to be swapped out
  *   to swap space and (later) to be read back into memory.
  * During disk I/O, PG_locked is used. This bit is set before I/O
- * and reset when I/O completes. page->wait is a wait queue of all
+ * and reset when I/O completes. page_waitqueue(page) is a wait queue of all
  * tasks waiting for the I/O on this page to complete.
  * PG_uptodate tells whether the page's contents is valid.
  * When a read completes, the page becomes uptodate, unless a disk I/O
@@ -299,6 +315,61 @@ typedef struct page {
 #define SetPageChecked(page)	set_bit(PG_checked, &(page)->flags)
 #define PageLaunder(page)	test_bit(PG_launder, &(page)->flags)
 #define SetPageLaunder(page)	set_bit(PG_launder, &(page)->flags)
+#define __SetPageReserved(page)	__set_bit(PG_reserved, &(page)->flags)
+
+/*
+ * The zone field is never updated after free_area_init_core()
+ * sets it, so none of the operations on it need to be atomic.
+ */
+#define NODE_SHIFT 4
+#define ZONE_SHIFT (BITS_PER_LONG - 8)
+
+struct zone_struct;
+extern struct zone_struct *zone_table[];
+
+static inline zone_t *page_zone(struct page *page)
+{
+	return zone_table[page->flags >> ZONE_SHIFT];
+}
+
+static inline void set_page_zone(struct page *page, unsigned long zone_num)
+{
+	page->flags &= ~(~0UL << ZONE_SHIFT);
+	page->flags |= zone_num << ZONE_SHIFT;
+}
+
+/*
+ * In order to avoid #ifdefs within C code itself, we define
+ * set_page_address to a noop for non-highmem machines, where
+ * the field isn't useful.
+ * The same is true for page_address() in arch-dependent code.
+ */
+#if defined(CONFIG_HIGHMEM) || defined(WANT_PAGE_VIRTUAL)
+
+#define set_page_address(page, address)			\
+	do {						\
+		(page)->virtual = (address);		\
+	} while(0)
+
+#else /* CONFIG_HIGHMEM || WANT_PAGE_VIRTUAL */
+#define set_page_address(page, address)  do { } while(0)
+#endif /* CONFIG_HIGHMEM || WANT_PAGE_VIRTUAL */
+
+/*
+ * Permanent address of a page. Obviously must never be
+ * called on a highmem page.
+ */
+#if defined(CONFIG_HIGHMEM) || defined(WANT_PAGE_VIRTUAL)
+
+#define page_address(page) ((page)->virtual)
+
+#else /* CONFIG_HIGHMEM || WANT_PAGE_VIRTUAL */
+
+#define page_address(page)						\
+	__va( (((page) - page_zone(page)->zone_mem_map) << PAGE_SHIFT)	\
+			+ page_zone(page)->zone_start_paddr)
+
+#endif /* CONFIG_HIGHMEM || WANT_PAGE_VIRTUAL */
 
 extern void FASTCALL(set_page_dirty(struct page *));
 

include/linux/mmzone.h

@@ -7,6 +7,7 @@
 #include <linux/config.h>
 #include <linux/spinlock.h>
 #include <linux/list.h>
+#include <linux/wait.h>
 
 /*
  * Free memory management - zoned buddy allocator.
@@ -47,6 +48,35 @@ typedef struct zone_struct {
 	 */
 	free_area_t		free_area[MAX_ORDER];
 
+	/*
+	 * wait_table		-- the array holding the hash table
+	 * wait_table_size	-- the size of the hash table array
+	 * wait_table_shift	-- wait_table_size
+	 * 				== BITS_PER_LONG (1 << wait_table_bits)
+	 *
+	 * The purpose of all these is to keep track of the people
+	 * waiting for a page to become available and make them
+	 * runnable again when possible. The trouble is that this
+	 * consumes a lot of space, especially when so few things
+	 * wait on pages at a given time. So instead of using
+	 * per-page waitqueues, we use a waitqueue hash table.
+	 *
+	 * The bucket discipline is to sleep on the same queue when
+	 * colliding and wake all in that wait queue when removing.
+	 * When something wakes, it must check to be sure its page is
+	 * truly available, a la thundering herd. The cost of a
+	 * collision is great, but given the expected load of the
+	 * table, they should be so rare as to be outweighed by the
+	 * benefits from the saved space.
+	 *
+	 * __wait_on_page() and unlock_page() in mm/filemap.c, are the
+	 * primary users of these fields, and in mm/page_alloc.c
+	 * free_area_init_core() performs the initialization of them.
+	 */
+	wait_queue_head_t	* wait_table;
+	unsigned long		wait_table_size;
+	unsigned long		wait_table_shift;
+
 	/*
 	 * Discontig memory support fields.
 	 */
@@ -132,11 +162,15 @@ extern pg_data_t contig_page_data;
 
 #define NODE_DATA(nid)		(&contig_page_data)
 #define NODE_MEM_MAP(nid)	mem_map
+#define MAX_NR_NODES		1
 
 #else /* !CONFIG_DISCONTIGMEM */
 
 #include <asm/mmzone.h>
 
+/* page->zone is currently 8 bits ... */
+#define MAX_NR_NODES		(255 / MAX_NR_ZONES)
+
 #endif /* !CONFIG_DISCONTIGMEM */
 
 #define MAP_ALIGN(x)	((((x) % sizeof(mem_map_t)) == 0) ? (x) : ((x) + \

include/linux/pagemap.h

@@ -97,6 +97,8 @@ static inline void wait_on_page(struct page * page)
 		___wait_on_page(page);
 }
 
+extern void wake_up_page(struct page *);
+
 extern struct page * grab_cache_page (struct address_space *, unsigned long);
 extern struct page * grab_cache_page_nowait (struct address_space *, unsigned long);
 

mm/Makefile

@@ -9,7 +9,7 @@
 
 O_TARGET := mm.o
 
-export-objs := shmem.o filemap.o mempool.o
+export-objs := shmem.o filemap.o mempool.o page_alloc.o
 
 obj-y	 := memory.o mmap.o filemap.o mprotect.o mlock.o mremap.o \
 	    vmalloc.o slab.o bootmem.o swap.o vmscan.o page_io.o \

mm/filemap.c

@@ -740,6 +740,67 @@ static int read_cluster_nonblocking(struct file * file, unsigned long offset,
 	return 0;
 }
 
+/*
+ * Knuth recommends primes in approximately golden ratio to the maximum
+ * integer representable by a machine word for multiplicative hashing.
+ * Chuck Lever verified the effectiveness of this technique:
+ * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
+ *
+ * These primes are chosen to be bit-sparse, that is operations on
+ * them can use shifts and additions instead of multiplications for
+ * machines where multiplications are slow.
+ */
+#if BITS_PER_LONG == 32
+/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
+#define GOLDEN_RATIO_PRIME 0x9e370001UL
+#elif BITS_PER_LONG == 64
+/*  2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
+#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
+#else
+#error Define GOLDEN_RATIO_PRIME for your wordsize.
+#endif
+
+/*
+ * In order to wait for pages to become available there must be
+ * waitqueues associated with pages. By using a hash table of
+ * waitqueues where the bucket discipline is to maintain all
+ * waiters on the same queue and wake all when any of the pages
+ * become available, and for the woken contexts to check to be
+ * sure the appropriate page became available, this saves space
+ * at a cost of "thundering herd" phenomena during rare hash
+ * collisions.
+ */
+static inline wait_queue_head_t *page_waitqueue(struct page *page)
+{
+	const zone_t *zone = page_zone(page);
+	wait_queue_head_t *wait = zone->wait_table;
+	unsigned long hash = (unsigned long)page;
+
+#if BITS_PER_LONG == 64
+	/*  Sigh, gcc can't optimise this alone like it does for 32 bits. */
+	unsigned long n = hash;
+	n <<= 18;
+	hash -= n;
+	n <<= 33;
+	hash -= n;
+	n <<= 3;
+	hash += n;
+	n <<= 3;
+	hash -= n;
+	n <<= 4;
+	hash += n;
+	n <<= 2;
+	hash += n;
+#else
+	/* On some cpus multiply is faster, on others gcc will do shifts */
+	hash *= GOLDEN_RATIO_PRIME;
+#endif
+
+	hash >>= zone->wait_table_shift;
+
+	return &wait[hash];
+}
+
 /* 
  * Wait for a page to get unlocked.
  *
@@ -749,10 +810,11 @@ static int read_cluster_nonblocking(struct file * file, unsigned long offset,
  */
 void ___wait_on_page(struct page *page)
 {
+	wait_queue_head_t *waitqueue = page_waitqueue(page);
 	struct task_struct *tsk = current;
 	DECLARE_WAITQUEUE(wait, tsk);
 
-	add_wait_queue(&page->wait, &wait);
+	add_wait_queue(waitqueue, &wait);
 	do {
 		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
 		if (!PageLocked(page))
@@ -760,19 +822,23 @@ void ___wait_on_page(struct page *page)
 		sync_page(page);
 		schedule();
 	} while (PageLocked(page));
-	tsk->state = TASK_RUNNING;
-	remove_wait_queue(&page->wait, &wait);
+	__set_task_state(tsk, TASK_RUNNING);
+	remove_wait_queue(waitqueue, &wait);
 }
 
+/*
+ * Unlock the page and wake up sleepers in ___wait_on_page.
+ */
 void unlock_page(struct page *page)
 {
+	wait_queue_head_t *waitqueue = page_waitqueue(page);
 	clear_bit(PG_launder, &(page)->flags);
 	smp_mb__before_clear_bit();
 	if (!test_and_clear_bit(PG_locked, &(page)->flags))
 		BUG();
 	smp_mb__after_clear_bit(); 
-	if (waitqueue_active(&(page)->wait))
-	wake_up(&(page)->wait);
+	if (waitqueue_active(waitqueue))
+		wake_up_all(waitqueue);
 }
 
 /*
@@ -781,10 +847,11 @@ void unlock_page(struct page *page)
  */
 static void __lock_page(struct page *page)
 {
+	wait_queue_head_t *waitqueue = page_waitqueue(page);
 	struct task_struct *tsk = current;
 	DECLARE_WAITQUEUE(wait, tsk);
 
-	add_wait_queue_exclusive(&page->wait, &wait);
+	add_wait_queue_exclusive(waitqueue, &wait);
 	for (;;) {
 		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
 		if (PageLocked(page)) {
@@ -794,10 +861,15 @@ static void __lock_page(struct page *page)
 		if (!TryLockPage(page))
 			break;
 	}
-	tsk->state = TASK_RUNNING;
-	remove_wait_queue(&page->wait, &wait);
+	__set_task_state(tsk, TASK_RUNNING);
+	remove_wait_queue(waitqueue, &wait);
 }
-	
+
+void wake_up_page(struct page *page)
+{
+	wake_up(page_waitqueue(page));
+}
+EXPORT_SYMBOL(wake_up_page);
 
 /*
  * Get an exclusive lock on the page, optimistically

mm/highmem.c

@@ -378,7 +378,7 @@ void create_bounce(unsigned long pfn, int gfp, struct bio **bio_orig)
 		/*
 		 * is destination page below bounce pfn?
 		 */
-		if ((page - page->zone->zone_mem_map) + (page->zone->zone_start_paddr >> PAGE_SHIFT) < pfn)
+		if ((page - page_zone(page)->zone_mem_map) + (page_zone(page)->zone_start_paddr >> PAGE_SHIFT) < pfn)
 			continue;
 
 		/*

mm/page_alloc.c

 /*
  *  linux/mm/page_alloc.c
  *
+ *  Manages the free list, the system allocates free pages here.
+ *  Note that kmalloc() lives in slab.c
+ *
  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  *  Swap reorganised 29.12.95, Stephen Tweedie
  *  Support of BIGMEM added by Gerhard Wichert, Siemens AG, July 1999
@@ -18,6 +21,7 @@
 #include <linux/bootmem.h>
 #include <linux/slab.h>
 #include <linux/compiler.h>
+#include <linux/module.h>
 
 int nr_swap_pages;
 int nr_active_pages;
@@ -26,6 +30,10 @@ struct list_head inactive_list;
 struct list_head active_list;
 pg_data_t *pgdat_list;
 
+/* Used to look up the address of the struct zone encoded in page->zone */
+zone_t *zone_table[MAX_NR_ZONES*MAX_NR_NODES];
+EXPORT_SYMBOL(zone_table);
+
 static char *zone_names[MAX_NR_ZONES] = { "DMA", "Normal", "HighMem" };
 static int zone_balance_ratio[MAX_NR_ZONES] __initdata = { 128, 128, 128, };
 static int zone_balance_min[MAX_NR_ZONES] __initdata = { 20 , 20, 20, };
@@ -54,12 +62,31 @@ static int zone_balance_max[MAX_NR_ZONES] __initdata = { 255 , 255, 255, };
 /*
  * Temporary debugging check.
  */
-#define BAD_RANGE(zone,x) (((zone) != (x)->zone) || (((x)-mem_map) < (zone)->zone_start_mapnr) || (((x)-mem_map) >= (zone)->zone_start_mapnr+(zone)->size))
+#define BAD_RANGE(zone, page)						\
+(									\
+	(((page) - mem_map) >= ((zone)->zone_start_mapnr+(zone)->size))	\
+	|| (((page) - mem_map) < (zone)->zone_start_mapnr)		\
+	|| ((zone) != page_zone(page))					\
+)
 
 /*
- * Buddy system. Hairy. You really aren't expected to understand this
+ * Freeing function for a buddy system allocator.
+ *
+ * The concept of a buddy system is to maintain direct-mapped table
+ * (containing bit values) for memory blocks of various "orders".
+ * The bottom level table contains the map for the smallest allocatable
+ * units of memory (here, pages), and each level above it describes
+ * pairs of units from the levels below, hence, "buddies".
+ * At a high level, all that happens here is marking the table entry
+ * at the bottom level available, and propagating the changes upward
+ * as necessary, plus some accounting needed to play nicely with other
+ * parts of the VM system.
+ *
+ * TODO: give references to descriptions of buddy system allocators,
+ * describe precisely the silly trick buddy allocators use to avoid
+ * storing an extra bit, utilizing entry point information.
  *
- * Hint: -mask = 1+~mask
+ * -- wli
  */
 
 static void FASTCALL(__free_pages_ok (struct page *page, unsigned int order));
@@ -90,7 +117,7 @@ static void __free_pages_ok (struct page *page, unsigned int order)
 		goto local_freelist;
  back_local_freelist:
 
-	zone = page->zone;
+	zone = page_zone(page);
 
 	mask = (~0UL) << order;
 	base = zone->zone_mem_map;
@@ -117,6 +144,8 @@ static void __free_pages_ok (struct page *page, unsigned int order)
 			break;
 		/*
 		 * Move the buddy up one level.
+		 * This code is taking advantage of the identity:
+		 * 	-mask = 1+~mask
 		 */
 		buddy1 = base + (page_idx ^ -mask);
 		buddy2 = base + page_idx;
@@ -255,7 +284,7 @@ static struct page * balance_classzone(zone_t * classzone, unsigned int gfp_mask
 			entry = local_pages->next;
 			do {
 				tmp = list_entry(entry, struct page, list);
-				if (tmp->index == order && memclass(tmp->zone, classzone)) {
+				if (tmp->index == order && memclass(page_zone(tmp), classzone)) {
 					list_del(entry);
 					current->nr_local_pages--;
 					set_page_count(tmp, 1);
@@ -625,6 +654,48 @@ static inline void build_zonelists(pg_data_t *pgdat)
 	} 
 }
 
+/*
+ * Helper functions to size the waitqueue hash table.
+ * Essentially these want to choose hash table sizes sufficiently
+ * large so that collisions trying to wait on pages are rare.
+ * But in fact, the number of active page waitqueues on typical
+ * systems is ridiculously low, less than 200. So this is even
+ * conservative, even though it seems large.
+ *
+ * The constant PAGES_PER_WAITQUEUE specifies the ratio of pages to
+ * waitqueues, i.e. the size of the waitq table given the number of pages.
+ */
+#define PAGES_PER_WAITQUEUE	256
+
+static inline unsigned long wait_table_size(unsigned long pages)
+{
+	unsigned long size = 1;
+
+	pages /= PAGES_PER_WAITQUEUE;
+
+	while (size < pages)
+		size <<= 1;
+
+	/*
+	 * Once we have dozens or even hundreds of threads sleeping
+	 * on IO we've got bigger problems than wait queue collision.
+	 * Limit the size of the wait table to a reasonable size.
+	 */
+	size = min(size, 4096UL);
+
+	return size;
+}
+
+/*
+ * This is an integer logarithm so that shifts can be used later
+ * to extract the more random high bits from the multiplicative
+ * hash function before the remainder is taken.
+ */
+static inline unsigned long wait_table_bits(unsigned long size)
+{
+	return ffz(~size);
+}
+
 #define LONG_ALIGN(x) (((x)+(sizeof(long))-1)&~((sizeof(long))-1))
 
 /*
@@ -637,7 +708,6 @@ void __init free_area_init_core(int nid, pg_data_t *pgdat, struct page **gmap,
 	unsigned long *zones_size, unsigned long zone_start_paddr, 
 	unsigned long *zholes_size, struct page *lmem_map)
 {
-	struct page *p;
 	unsigned long i, j;
 	unsigned long map_size;
 	unsigned long totalpages, offset, realtotalpages;
@@ -680,24 +750,13 @@ void __init free_area_init_core(int nid, pg_data_t *pgdat, struct page **gmap,
 	pgdat->node_start_mapnr = (lmem_map - mem_map);
 	pgdat->nr_zones = 0;
 
-	/*
-	 * Initially all pages are reserved - free ones are freed
-	 * up by free_all_bootmem() once the early boot process is
-	 * done.
-	 */
-	for (p = lmem_map; p < lmem_map + totalpages; p++) {
-		set_page_count(p, 0);
-		SetPageReserved(p);
-		init_waitqueue_head(&p->wait);
-		memlist_init(&p->list);
-	}
-
 	offset = lmem_map - mem_map;	
 	for (j = 0; j < MAX_NR_ZONES; j++) {
 		zone_t *zone = pgdat->node_zones + j;
 		unsigned long mask;
 		unsigned long size, realsize;
 
+		zone_table[nid * MAX_NR_ZONES + j] = zone;
 		realsize = size = zones_size[j];
 		if (zholes_size)
 			realsize -= zholes_size[j];
@@ -712,6 +771,20 @@ void __init free_area_init_core(int nid, pg_data_t *pgdat, struct page **gmap,
 		if (!size)
 			continue;
 
+		/*
+		 * The per-page waitqueue mechanism uses hashed waitqueues
+		 * per zone.
+		 */
+		zone->wait_table_size = wait_table_size(size);
+		zone->wait_table_shift =
+			BITS_PER_LONG - wait_table_bits(zone->wait_table_size);
+		zone->wait_table = (wait_queue_head_t *)
+			alloc_bootmem_node(pgdat, zone->wait_table_size
+						* sizeof(wait_queue_head_t));
+
+		for(i = 0; i < zone->wait_table_size; ++i)
+			init_waitqueue_head(zone->wait_table + i);
+
 		pgdat->nr_zones = j+1;
 
 		mask = (realsize / zone_balance_ratio[j]);
@@ -730,11 +803,19 @@ void __init free_area_init_core(int nid, pg_data_t *pgdat, struct page **gmap,
 		if ((zone_start_paddr >> PAGE_SHIFT) & (zone_required_alignment-1))
 			printk("BUG: wrong zone alignment, it will crash\n");
 
+		/*
+		 * Initially all pages are reserved - free ones are freed
+		 * up by free_all_bootmem() once the early boot process is
+		 * done. Non-atomic initialization, single-pass.
+		 */
 		for (i = 0; i < size; i++) {
 			struct page *page = mem_map + offset + i;
-			page->zone = zone;
+			set_page_zone(page, nid * MAX_NR_ZONES + j);
+			init_page_count(page);
+			__SetPageReserved(page);
+			memlist_init(&page->list);
 			if (j != ZONE_HIGHMEM)
-				page->virtual = __va(zone_start_paddr);
+				set_page_address(page, __va(zone_start_paddr));
 			zone_start_paddr += PAGE_SIZE;
 		}
 

mm/vmscan.c

@@ -59,7 +59,7 @@ static inline int try_to_swap_out(struct mm_struct * mm, struct vm_area_struct*
 		return 0;
 
 	/* Don't bother replenishing zones not under pressure.. */
-	if (!memclass(page->zone, classzone))
+	if (!memclass(page_zone(page), classzone))
 		return 0;
 
 	if (TryLockPage(page))
@@ -370,7 +370,7 @@ static int shrink_cache(int nr_pages, zone_t * classzone, unsigned int gfp_mask,
 		if (unlikely(!page_count(page)))
 			continue;
 
-		if (!memclass(page->zone, classzone))
+		if (!memclass(page_zone(page), classzone))
 			continue;
 
 		/* Racy check to avoid trylocking when not worthwhile */