alloc: use page numbers in lists to reduce overhead.
authorRusty Russell <rusty@rustcorp.com.au>
Wed, 9 Jun 2010 14:16:03 +0000 (23:46 +0930)
committerRusty Russell <rusty@rustcorp.com.au>
Wed, 9 Jun 2010 14:16:03 +0000 (23:46 +0930)
ccan/alloc/alloc.c

index 1b011caaf1df45a09f402b7399f98d834af00069..3f1cc75008c907e843c2b0d69f06cded79021b02 100644 (file)
 #endif
 
 /* Smallest pool size for this scheme: 512-byte small pages.  That's
- * 4/8% overhead for 32/64 bit. */
+ * 3/5% overhead for 32/64 bit. */
 #define MIN_USEFUL_SIZE (MAX_PAGES << (9 + BITS_FROM_SMALL_TO_LARGE_PAGE))
 
 /* Every 4 buckets, we jump up a power of 2. ...8 10 12 14 16 20 24 28 32... */
 #define INTER_BUCKET_SPACE 4
 
+#define SMALL_PAGES_PER_LARGE_PAGE (1 << BITS_FROM_SMALL_TO_LARGE_PAGE)
+
 /* FIXME: Figure this out properly. */
 #define MAX_SIZE (1 << 30)
 
 
 struct bucket_state {
        unsigned long elements_per_page;
-       unsigned long page_list;
-       unsigned long full_list;
+       u16 page_list;
+       u16 full_list;
 };
 
 struct header {
-       /* 1024 bit bitmap of which pages are large. */
+       /* Bitmap of which pages are large. */
        unsigned long pagesize[MAX_PAGES / BITS_PER_LONG];
 
        /* List of unused small/large pages. */
-       unsigned long small_free_list;
-       unsigned long large_free_list;
+       u16 small_free_list;
+       u16 large_free_list;
 
        /* This is less defined: we have two buckets for each power of 2 */
        struct bucket_state bs[1];
 };
 
 struct page_header {
-       unsigned long next, prev;
+       u16 next, prev;
        u32 elements_used;
        /* FIXME: Pack this in somewhere... */
        u8 bucket;
@@ -275,14 +277,16 @@ static unsigned long align_up(unsigned long x, unsigned long align)
        return (x + align - 1) & ~(align - 1);
 }
 
-static struct page_header *from_off(struct header *head, unsigned long off)
+static struct page_header *from_pgnum(struct header *head,
+                                     unsigned long pgnum,
+                                     unsigned sp_bits)
 {
-       return (struct page_header *)((char *)head + off);
+       return (struct page_header *)((char *)head + (pgnum << sp_bits));
 }
 
-static unsigned long to_off(struct header *head, void *p)
+static u16 to_pgnum(struct header *head, void *p, unsigned sp_bits)
 {
-       return (char *)p - (char *)head;
+       return ((char *)p - (char *)head) >> sp_bits;
 }
 
 static size_t used_size(unsigned int num_elements)
@@ -307,13 +311,13 @@ static unsigned long page_header_size(unsigned int align_bits,
 }
 
 static void add_to_list(struct header *head,
-                       unsigned long *list, struct page_header *ph)
+                       u16 *list, struct page_header *ph, unsigned sp_bits)
 {
-       unsigned long h = *list, offset = to_off(head, ph);
+       unsigned long h = *list, offset = to_pgnum(head, ph, sp_bits);
 
        ph->next = h;
        if (h) {
-               struct page_header *prev = from_off(head, h);
+               struct page_header *prev = from_pgnum(head, h, sp_bits);
                assert(prev->prev == 0);
                prev->prev = offset;
        }
@@ -322,75 +326,80 @@ static void add_to_list(struct header *head,
 }
 
 static void del_from_list(struct header *head,
-                         unsigned long *list, struct page_header *ph)
+                         u16 *list, struct page_header *ph, unsigned sp_bits)
 {
        /* Front of list? */
        if (ph->prev == 0) {
                *list = ph->next;
        } else {
-               struct page_header *prev = from_off(head, ph->prev);
+               struct page_header *prev = from_pgnum(head, ph->prev, sp_bits);
                prev->next = ph->next;
        }
        if (ph->next != 0) {
-               struct page_header *next = from_off(head, ph->next);
+               struct page_header *next = from_pgnum(head, ph->next, sp_bits);
                next->prev = ph->prev;
        }
 }
 
-static unsigned long pop_from_list(struct header *head,
-                                  unsigned long *list)
+static u16 pop_from_list(struct header *head,
+                                  u16 *list,
+                                  unsigned int sp_bits)
 {
-       unsigned long h = *list;
-       struct page_header *ph = from_off(head, h);
+       u16 h = *list;
+       struct page_header *ph = from_pgnum(head, h, sp_bits);
 
        if (likely(h)) {
                *list = ph->next;
-               if (*list) {
-                       struct page_header *next = from_off(head, *list);
-                       next->prev = 0;
-               }
+               if (*list)
+                       from_pgnum(head, *list, sp_bits)->prev = 0;
        }
        return h;
 }
 
 static void add_small_page_to_freelist(struct header *head,
-                                      struct page_header *ph)
+                                      struct page_header *ph,
+                                      unsigned int sp_bits)
 {
-       add_to_list(head, &head->small_free_list, ph);
+       add_to_list(head, &head->small_free_list, ph, sp_bits);
 }
 
 static void add_large_page_to_freelist(struct header *head,
-                                      struct page_header *ph)
+                                      struct page_header *ph,
+                                      unsigned int sp_bits)
 {
-       add_to_list(head, &head->large_free_list, ph);
+       add_to_list(head, &head->large_free_list, ph, sp_bits);
 }
 
 static void add_to_bucket_list(struct header *head,
                               struct bucket_state *bs,
-                              struct page_header *ph)
+                              struct page_header *ph,
+                              unsigned int sp_bits)
 {
-       add_to_list(head, &bs->page_list, ph);
+       add_to_list(head, &bs->page_list, ph, sp_bits);
 }
 
 static void del_from_bucket_list(struct header *head,
                                 struct bucket_state *bs,
-                                struct page_header *ph)
+                                struct page_header *ph,
+                                unsigned int sp_bits)
 {
-       del_from_list(head, &bs->page_list, ph);
+       del_from_list(head, &bs->page_list, ph, sp_bits);
 }
 
 static void del_from_bucket_full_list(struct header *head,
                                      struct bucket_state *bs,
-                                     struct page_header *ph)
+                                     struct page_header *ph,
+                                     unsigned int sp_bits)
 {
-       del_from_list(head, &bs->full_list, ph);
+       del_from_list(head, &bs->full_list, ph, sp_bits);
 }
 
 static void add_to_bucket_full_list(struct header *head,
                                    struct bucket_state *bs,
-                                   struct page_header *ph)
+                                   struct page_header *ph,
+                                   unsigned int sp_bits)
 {
-       add_to_list(head, &bs->full_list, ph);
+       add_to_list(head, &bs->full_list, ph, sp_bits);
 }
 
 static void clear_bit(unsigned long bitmap[], unsigned int off)
@@ -433,12 +442,10 @@ static unsigned long elements_per_page(unsigned long align_bits,
        return num;
 }
 
-static bool large_page_bucket(unsigned int bucket, unsigned long poolsize)
+static bool large_page_bucket(unsigned int bucket, unsigned int sp_bits)
 {
-       unsigned int sp_bits;
        unsigned long max_smallsize;
 
-       sp_bits = large_page_bits(poolsize) - BITS_FROM_SMALL_TO_LARGE_PAGE;
        /* Note: this doesn't take into account page header. */
        max_smallsize = (1UL << sp_bits) >> MAX_PAGE_OBJECT_ORDER;
 
@@ -462,6 +469,9 @@ void alloc_init(void *pool, unsigned long poolsize)
                return;
        }
 
+       /* We rely on page numbers fitting in 16 bit. */
+       BUILD_ASSERT((MAX_PAGES << BITS_FROM_SMALL_TO_LARGE_PAGE) < 65536);
+       
        lp_bits = large_page_bits(poolsize);
        sp_bits = lp_bits - BITS_FROM_SMALL_TO_LARGE_PAGE;
 
@@ -474,7 +484,7 @@ void alloc_init(void *pool, unsigned long poolsize)
        for (i = 0; i < num_buckets; i++) {
                unsigned long pagesize;
 
-               if (large_page_bucket(i, poolsize))
+               if (large_page_bucket(i, sp_bits))
                        pagesize = 1UL << lp_bits;
                else
                        pagesize = 1UL << sp_bits;
@@ -495,20 +505,20 @@ void alloc_init(void *pool, unsigned long poolsize)
 
        /* Skip over page(s) used by header, add rest to free list */
        for (i = align_up(header_size, (1 << sp_bits)) >> sp_bits;
-            i < (1 << BITS_FROM_SMALL_TO_LARGE_PAGE);
+            i < SMALL_PAGES_PER_LARGE_PAGE;
             i++) {
-               ph = from_off(head, i<<sp_bits);
+               ph = from_pgnum(head, i, sp_bits);
                ph->elements_used = 0;
-               add_small_page_to_freelist(head, ph);
+               add_small_page_to_freelist(head, ph, sp_bits);
        }
 
        /* Add the rest of the pages as large pages. */
-       i = (1 << lp_bits);
-       while (i + (1 << lp_bits) <= poolsize) {
-               ph = from_off(head, i);
+       i = SMALL_PAGES_PER_LARGE_PAGE;
+       while ((i << sp_bits) + (1 << lp_bits) <= poolsize) {
+               ph = from_pgnum(head, i, sp_bits);
                ph->elements_used = 0;
-               add_large_page_to_freelist(head, ph);
-               i += (1 << lp_bits);
+               add_large_page_to_freelist(head, ph, sp_bits);
+               i += SMALL_PAGES_PER_LARGE_PAGE;
        }
 }
 
@@ -519,82 +529,85 @@ static void del_large_from_small_free_list(struct header *head,
 {
        unsigned long i;
 
-       for (i = 0; i < (1 << BITS_FROM_SMALL_TO_LARGE_PAGE); i++) {
+       for (i = 0; i < SMALL_PAGES_PER_LARGE_PAGE; i++) {
                del_from_list(head, &head->small_free_list,
-                             (void *)ph + (i << sp_bits));
+                             (void *)ph + (i << sp_bits),
+                             sp_bits);
        }
 }
 
-static bool all_empty(struct header *head, unsigned long off, unsigned sp_bits)
+static bool all_empty(struct header *head,
+                     unsigned long pgnum,
+                     unsigned sp_bits)
 {
        unsigned long i;
 
-       for (i = 0; i < (1 << BITS_FROM_SMALL_TO_LARGE_PAGE); i++) {
-               struct page_header *ph = from_off(head, off + (i << sp_bits));
+       for (i = 0; i < SMALL_PAGES_PER_LARGE_PAGE; i++) {
+               struct page_header *ph = from_pgnum(head, pgnum + i, sp_bits);
                if (ph->elements_used)
                        return false;
        }
        return true;
 }
 
-static unsigned long get_large_page(struct header *head,
-                                   unsigned long poolsize)
+static u16 get_large_page(struct header *head, unsigned long poolsize,
+                         unsigned int sp_bits)
 {
-       unsigned long lp_bits, sp_bits, i, page;
+       unsigned int lp_bits, i, page;
+
+       lp_bits = sp_bits + BITS_FROM_SMALL_TO_LARGE_PAGE;
 
-       page = pop_from_list(head, &head->large_free_list);
+       page = pop_from_list(head, &head->large_free_list, sp_bits);
        if (likely(page))
                return page;
 
        /* Look for small pages to coalesce, after first large page. */
-       lp_bits = large_page_bits(poolsize);
-       sp_bits = lp_bits - BITS_FROM_SMALL_TO_LARGE_PAGE;
-
-       for (i = (1 << lp_bits); i < poolsize; i += (1 << lp_bits)) {
+       for (i = SMALL_PAGES_PER_LARGE_PAGE;
+            i < (poolsize >> lp_bits) << BITS_FROM_SMALL_TO_LARGE_PAGE;
+            i += SMALL_PAGES_PER_LARGE_PAGE) {
                /* Already a large page? */
-               if (test_bit(head->pagesize, i >> lp_bits))
+               if (test_bit(head->pagesize, i / SMALL_PAGES_PER_LARGE_PAGE))
                        continue;
                if (all_empty(head, i, sp_bits)) {
-                       struct page_header *ph = from_off(head, i);
-                       set_bit(head->pagesize, i >> lp_bits);
+                       struct page_header *ph = from_pgnum(head, i, sp_bits);
+                       set_bit(head->pagesize,
+                               i / SMALL_PAGES_PER_LARGE_PAGE);
                        del_large_from_small_free_list(head, ph, sp_bits);
-                       add_large_page_to_freelist(head, ph);
+                       add_large_page_to_freelist(head, ph, sp_bits);
                }
        }
                        
-       return pop_from_list(head, &head->large_free_list);
+       return pop_from_list(head, &head->large_free_list, sp_bits);
 }
 
 /* Returns small page. */
 static unsigned long break_up_large_page(struct header *head,
-                                        unsigned long psize,
-                                        unsigned long lpage)
+                                        unsigned int sp_bits,
+                                        u16 lpage)
 {
-       unsigned long lp_bits, sp_bits, i;
+       unsigned int i;
 
-       lp_bits = large_page_bits(psize);
-       sp_bits = lp_bits - BITS_FROM_SMALL_TO_LARGE_PAGE;
-       clear_bit(head->pagesize, lpage >> lp_bits);
+       clear_bit(head->pagesize, lpage >> BITS_FROM_SMALL_TO_LARGE_PAGE);
 
-       for (i = 1; i < (1 << BITS_FROM_SMALL_TO_LARGE_PAGE); i++)
-               add_small_page_to_freelist(head,
-                                          from_off(head,
-                                                   lpage + (i<<sp_bits)));
+       for (i = 1; i < SMALL_PAGES_PER_LARGE_PAGE; i++) {
+               struct page_header *ph = from_pgnum(head, lpage + i, sp_bits);
+               add_small_page_to_freelist(head, ph, sp_bits);
+       }
 
        return lpage;
 }
 
-static unsigned long get_small_page(struct header *head,
-                                   unsigned long poolsize)
+static u16 get_small_page(struct header *head, unsigned long poolsize,
+                         unsigned int sp_bits)
 {
-       unsigned long ret;
+       u16 ret;
 
-       ret = pop_from_list(head, &head->small_free_list);
+       ret = pop_from_list(head, &head->small_free_list, sp_bits);
        if (likely(ret))
                return ret;
-       ret = get_large_page(head, poolsize);
+       ret = get_large_page(head, poolsize, sp_bits);
        if (likely(ret))
-               ret = break_up_large_page(head, poolsize, ret);
+               ret = break_up_large_page(head, sp_bits, ret);
        return ret;
 }
 
@@ -606,6 +619,7 @@ void *alloc_get(void *pool, unsigned long poolsize,
        unsigned long i;
        struct bucket_state *bs;
        struct page_header *ph;
+       unsigned int sp_bits;
 
        if (poolsize < MIN_USEFUL_SIZE) {
                return tiny_alloc_get(pool, poolsize, size, align);
@@ -622,25 +636,28 @@ void *alloc_get(void *pool, unsigned long poolsize,
        }
 
        bs = &head->bs[bucket];
+       sp_bits = large_page_bits(poolsize) - BITS_FROM_SMALL_TO_LARGE_PAGE;
 
        if (!bs->page_list) {
                struct page_header *ph;
 
-               if (large_page_bucket(bucket, poolsize))
-                       bs->page_list = get_large_page(head, poolsize);
+               if (large_page_bucket(bucket, sp_bits))
+                       bs->page_list = get_large_page(head, poolsize,
+                                                      sp_bits);
                else
-                       bs->page_list = get_small_page(head, poolsize);
+                       bs->page_list = get_small_page(head, poolsize,
+                                                      sp_bits);
                /* FIXME: Try large-aligned alloc?  Header stuffing? */
                if (unlikely(!bs->page_list))
                        return NULL;
-               ph = from_off(head, bs->page_list);
+               ph = from_pgnum(head, bs->page_list, sp_bits);
                ph->bucket = bucket;
                ph->elements_used = 0;
                ph->next = 0;
                memset(ph->used, 0, used_size(bs->elements_per_page));
        }
 
-       ph = from_off(head, bs->page_list);
+       ph = from_pgnum(head, bs->page_list, sp_bits);
 
        i = find_free_bit(ph->used);
        set_bit(ph->used, i);
@@ -648,8 +665,8 @@ void *alloc_get(void *pool, unsigned long poolsize,
 
        /* check if this page is now full */
        if (unlikely(ph->elements_used == bs->elements_per_page)) {
-               del_from_bucket_list(head, bs, ph);
-               add_to_bucket_full_list(head, bs, ph);
+               del_from_bucket_list(head, bs, ph, sp_bits);
+               add_to_bucket_full_list(head, bs, ph, sp_bits);
        }
 
        return (char *)ph + page_header_size(ph->bucket / INTER_BUCKET_SPACE,
@@ -661,33 +678,36 @@ void alloc_free(void *pool, unsigned long poolsize, void *free)
 {
        struct header *head = pool;
        struct bucket_state *bs;
-       unsigned int pagebits;
-       unsigned long i, pgoffset, offset = (char *)free - (char *)pool;
+       unsigned int sp_bits;
+       unsigned long i, pgnum, pgoffset, offset = (char *)free - (char *)pool;
        bool smallpage;
        struct page_header *ph;
 
        if (poolsize < MIN_USEFUL_SIZE) {
                return tiny_alloc_free(pool, poolsize, free);
        }
-
+       
        /* Get page header. */
-       pagebits = large_page_bits(poolsize);
-       if (!test_bit(head->pagesize, offset >> pagebits)) {
-               smallpage = true;
-               pagebits -= BITS_FROM_SMALL_TO_LARGE_PAGE;
-       } else
+       sp_bits = large_page_bits(poolsize) - BITS_FROM_SMALL_TO_LARGE_PAGE;
+       pgnum = offset >> sp_bits;
+
+       /* Big page? Round down further. */
+       if (test_bit(head->pagesize, pgnum >> BITS_FROM_SMALL_TO_LARGE_PAGE)) {
                smallpage = false;
+               pgnum &= ~(SMALL_PAGES_PER_LARGE_PAGE - 1);
+       } else
+               smallpage = true;
 
        /* Step back to page header. */
-       ph = from_off(head, offset & ~((1UL << pagebits) - 1));
+       ph = from_pgnum(head, pgnum, sp_bits);
        bs = &head->bs[ph->bucket];
-       pgoffset = (offset & ((1UL << pagebits) - 1))
+       pgoffset = offset - (pgnum << sp_bits)
                - page_header_size(ph->bucket / INTER_BUCKET_SPACE,
                                   bs->elements_per_page);
 
        if (unlikely(ph->elements_used == bs->elements_per_page)) {
-               del_from_bucket_full_list(head, bs, ph);
-               add_to_bucket_list(head, bs, ph);
+               del_from_bucket_full_list(head, bs, ph, sp_bits);
+               add_to_bucket_list(head, bs, ph, sp_bits);
        }
 
        /* Which element are we? */
@@ -697,18 +717,18 @@ void alloc_free(void *pool, unsigned long poolsize, void *free)
 
        if (unlikely(ph->elements_used == 0)) {
                bs = &head->bs[ph->bucket];
-               del_from_bucket_list(head, bs, ph);
+               del_from_bucket_list(head, bs, ph, sp_bits);
                if (smallpage)
-                       add_small_page_to_freelist(head, ph);
+                       add_small_page_to_freelist(head, ph, sp_bits);
                else
-                       add_large_page_to_freelist(head, ph);
+                       add_large_page_to_freelist(head, ph, sp_bits);
        }
 }
 
 unsigned long alloc_size(void *pool, unsigned long poolsize, void *p)
 {
        struct header *head = pool;
-       unsigned int pagebits;
+       unsigned int pgnum, sp_bits;
        unsigned long offset = (char *)p - (char *)pool;
        struct page_header *ph;
 
@@ -716,12 +736,15 @@ unsigned long alloc_size(void *pool, unsigned long poolsize, void *p)
                return tiny_alloc_size(pool, poolsize, p);
 
        /* Get page header. */
-       pagebits = large_page_bits(poolsize);
-       if (!test_bit(head->pagesize, offset >> pagebits))
-               pagebits -= BITS_FROM_SMALL_TO_LARGE_PAGE;
+       sp_bits = large_page_bits(poolsize) - BITS_FROM_SMALL_TO_LARGE_PAGE;
+       pgnum = offset >> sp_bits;
+
+       /* Big page? Round down further. */
+       if (test_bit(head->pagesize, pgnum >> BITS_FROM_SMALL_TO_LARGE_PAGE))
+               pgnum &= ~(SMALL_PAGES_PER_LARGE_PAGE - 1);
 
        /* Step back to page header. */
-       ph = from_off(head, offset & ~((1UL << pagebits) - 1));
+       ph = from_pgnum(head, pgnum, sp_bits);
        return bucket_to_size(ph->bucket);
 }
 
@@ -748,11 +771,18 @@ static unsigned long count_bits(const unsigned long bitmap[],
        return count;
 }
 
-static bool out_of_bounds(unsigned long off,
+static bool out_of_bounds(unsigned long pgnum,
+                         unsigned int sp_bits,
                          unsigned long pagesize,
                          unsigned long poolsize)
 {
-       return (off > poolsize || off + pagesize > poolsize);
+       if (((pgnum << sp_bits) >> sp_bits) != pgnum)
+               return true;
+
+       if ((pgnum << sp_bits) > poolsize)
+               return true;
+
+       return ((pgnum << sp_bits) + pagesize > poolsize);
 }
 
 static bool check_bucket(struct header *head,
@@ -761,13 +791,15 @@ static bool check_bucket(struct header *head,
                         struct bucket_state *bs,
                         unsigned int bindex)
 {
-       bool lp_bucket = large_page_bucket(bindex, poolsize);
+       bool lp_bucket;
        struct page_header *ph;
        unsigned long taken, i, prev, pagesize, sp_bits, lp_bits;
 
        lp_bits = large_page_bits(poolsize);
        sp_bits = lp_bits - BITS_FROM_SMALL_TO_LARGE_PAGE;
 
+       lp_bucket = large_page_bucket(bindex, sp_bits);
+
        pagesize = 1UL << (lp_bucket ? lp_bits : sp_bits);
 
        /* This many elements fit? */
@@ -788,22 +820,23 @@ static bool check_bucket(struct header *head,
        prev = 0;
        for (i = bs->page_list; i; i = ph->next) {
                /* Bad pointer? */
-               if (out_of_bounds(i, pagesize, poolsize))
+               if (out_of_bounds(i, sp_bits, pagesize, poolsize))
                        return check_fail();
                /* Wrong size page? */
-               if (!!test_bit(head->pagesize, i >> lp_bits) != lp_bucket)
+               if (!!test_bit(head->pagesize, i >> BITS_FROM_SMALL_TO_LARGE_PAGE)
+                   != lp_bucket)
                        return check_fail();
-               /* Not page boundary? */
-               if (i % pagesize)
+               /* Large page not on boundary? */
+               if (lp_bucket && (i % SMALL_PAGES_PER_LARGE_PAGE) != 0)
                        return check_fail();
-               ph = from_off(head, i);
+               ph = from_pgnum(head, i, sp_bits);
                /* Linked list corrupt? */
                if (ph->prev != prev)
                        return check_fail();
                /* Already seen this page? */
-               if (test_bit(pages, i >> sp_bits))
+               if (test_bit(pages, i))
                        return check_fail();
-               set_bit(pages, i >> sp_bits);
+               set_bit(pages, i);
                /* Empty or full? */
                if (ph->elements_used == 0)
                        return check_fail();
@@ -823,22 +856,22 @@ static bool check_bucket(struct header *head,
        prev = 0;
        for (i = bs->full_list; i; i = ph->next) {
                /* Bad pointer? */
-               if (out_of_bounds(i, pagesize, poolsize))
+               if (out_of_bounds(i, sp_bits, pagesize, poolsize))
                        return check_fail();
                /* Wrong size page? */
-               if (!!test_bit(head->pagesize, i >> lp_bits) != lp_bucket)
+               if (!!test_bit(head->pagesize, i >> BITS_FROM_SMALL_TO_LARGE_PAGE)
+                   != lp_bucket)
+               /* Large page not on boundary? */
+               if (lp_bucket && (i % SMALL_PAGES_PER_LARGE_PAGE) != 0)
                        return check_fail();
-               /* Not page boundary? */
-               if (i % pagesize)
-                       return check_fail();
-               ph = from_off(head, i);
+               ph = from_pgnum(head, i, sp_bits);
                /* Linked list corrupt? */
                if (ph->prev != prev)
                        return check_fail();
                /* Already seen this page? */
-               if (test_bit(pages, i >> sp_bits))
+               if (test_bit(pages, i))
                        return check_fail();
-               set_bit(pages, i >> sp_bits);
+               set_bit(pages, i);
                /* Not full? */
                if (ph->elements_used != bs->elements_per_page)
                        return check_fail();
@@ -880,22 +913,19 @@ bool alloc_check(void *pool, unsigned long poolsize)
        prev = 0;
        for (i = head->small_free_list; i; i = ph->next) {
                /* Bad pointer? */
-               if (out_of_bounds(i, 1 << sp_bits, poolsize))
+               if (out_of_bounds(i, sp_bits, 1 << sp_bits, poolsize))
                        return check_fail();
                /* Large page? */
-               if (test_bit(head->pagesize, i >> lp_bits))
+               if (test_bit(head->pagesize, i >> BITS_FROM_SMALL_TO_LARGE_PAGE))
                        return check_fail();
-               /* Not page boundary? */
-               if (i % (1 << sp_bits))
-                       return check_fail();
-               ph = from_off(head, i);
+               ph = from_pgnum(head, i, sp_bits);
                /* Linked list corrupt? */
                if (ph->prev != prev)
                        return check_fail();
                /* Already seen this page? */
-               if (test_bit(pages, i >> sp_bits))
+               if (test_bit(pages, i))
                        return check_fail();
-               set_bit(pages, i >> sp_bits);
+               set_bit(pages, i);
                prev = i;
        }
 
@@ -903,22 +933,22 @@ bool alloc_check(void *pool, unsigned long poolsize)
        prev = 0;
        for (i = head->large_free_list; i; i = ph->next) {
                /* Bad pointer? */
-               if (out_of_bounds(i, 1 << lp_bits, poolsize))
+               if (out_of_bounds(i, sp_bits, 1 << lp_bits, poolsize))
                        return check_fail();
                /* Not large page? */
-               if (!test_bit(head->pagesize, i >> lp_bits))
+               if (!test_bit(head->pagesize, i >> BITS_FROM_SMALL_TO_LARGE_PAGE))
                        return check_fail();
                /* Not page boundary? */
-               if (i % (1 << lp_bits))
+               if ((i % SMALL_PAGES_PER_LARGE_PAGE) != 0)
                        return check_fail();
-               ph = from_off(head, i);
+               ph = from_pgnum(head, i, sp_bits);
                /* Linked list corrupt? */
                if (ph->prev != prev)
                        return check_fail();
                /* Already seen this page? */
-               if (test_bit(pages, i >> sp_bits))
+               if (test_bit(pages, i))
                        return check_fail();
-               set_bit(pages, i >> sp_bits);
+               set_bit(pages, i);
                prev = i;
        }
 
@@ -937,7 +967,7 @@ bool alloc_check(void *pool, unsigned long poolsize)
                if (test_bit(head->pagesize,
                             i >> BITS_FROM_SMALL_TO_LARGE_PAGE)) {
                        /* Large page, skip rest. */
-                       i += (1 << BITS_FROM_SMALL_TO_LARGE_PAGE) - 1;
+                       i += SMALL_PAGES_PER_LARGE_PAGE - 1;
                }
        }
 
@@ -954,25 +984,27 @@ static unsigned long print_overhead(FILE *out, const char *desc,
 }
 
 static unsigned long count_list(struct header *head,
-                               unsigned long off,
+                               u16 pgnum,
+                               unsigned int sp_bits,
                                unsigned long *total_elems)
 {
        struct page_header *p;
        unsigned long ret = 0;
 
-       while (off) {
-               p = from_off(head, off);
+       while (pgnum) {
+               p = from_pgnum(head, pgnum, sp_bits);
                if (total_elems)
                        (*total_elems) += p->elements_used;
                ret++;
-               off = p->next;
+               pgnum = p->next;
        }
        return ret;
 }
 
 static unsigned long visualize_bucket(FILE *out, struct header *head,
                                      unsigned int bucket,
-                                     unsigned long poolsize)
+                                     unsigned long poolsize,
+                                     unsigned int sp_bits)
 {
        unsigned long num_full, num_partial, num_pages, page_size,
                elems, hdr_min, hdr_size, elems_per_page, overhead = 0;
@@ -987,8 +1019,10 @@ static unsigned long visualize_bucket(FILE *out, struct header *head,
                                    elems_per_page);
 
        elems = 0;
-       num_full = count_list(head, head->bs[bucket].full_list, &elems);
-       num_partial = count_list(head, head->bs[bucket].page_list, &elems);
+       num_full = count_list(head, head->bs[bucket].full_list, sp_bits,
+                             &elems);
+       num_partial = count_list(head, head->bs[bucket].page_list, sp_bits,
+                                &elems);
        num_pages = num_full + num_partial;
        if (!num_pages)
                return 0;
@@ -1003,9 +1037,9 @@ static unsigned long visualize_bucket(FILE *out, struct header *head,
        overhead += print_overhead(out, "page post-header alignments",
                                   (hdr_size - hdr_min) * num_pages, poolsize);
        /* Between last element and end of page. */
-       page_size = 1UL << large_page_bits(poolsize);
-       if (!large_page_bucket(bucket, poolsize))
-               page_size >>= BITS_FROM_SMALL_TO_LARGE_PAGE;
+       page_size = (1 << sp_bits);
+       if (large_page_bucket(bucket, sp_bits))
+               page_size <<= BITS_FROM_SMALL_TO_LARGE_PAGE;
 
        overhead += print_overhead(out, "page tails",
                                   (page_size - (hdr_size
@@ -1051,21 +1085,21 @@ void alloc_visualize(FILE *out, void *pool, unsigned long poolsize)
        /* Total large pages. */
        i = count_bits(head->pagesize, poolsize >> lp_bits);
        /* Used pages. */
-       count = i - count_list(head, head->large_free_list, NULL);
+       count = i - count_list(head, head->large_free_list, sp_bits, NULL);
        fprintf(out, "%lu/%lu large pages used (%.3g%%)\n",
                count, i, count ? 100.0 * count / i : 0.0);
 
        /* Total small pages. */
        i = (poolsize >> lp_bits) - i;
        /* Used pages */
-       count = i - count_list(head, head->small_free_list, NULL);
+       count = i - count_list(head, head->small_free_list, sp_bits, NULL);
        fprintf(out, "%lu/%lu small pages used (%.3g%%)\n",
                count, i, count ? 100.0 * count / i : 0.0);
 
        /* Summary of each bucket. */
        fprintf(out, "%lu buckets:\n", num_buckets);
        for (i = 0; i < num_buckets; i++)
-               overhead += visualize_bucket(out, head, i, poolsize);
+               overhead += visualize_bucket(out, head, i, poolsize, sp_bits);
 
        print_overhead(out, "total", overhead, poolsize);
 }