[Xen-changelog] [xen-unstable] xmalloc: use tlsf algorithm

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1224151790 -3600
# Node ID 48fba1dbcfaf1f591e457780f7fad9b54ef39e58
# Parent  98ff908a91b7e12d7ddc609853fa1237d1714dec
xmalloc: use tlsf algorithm

This patch replaces the Xen xmalloc engine with tlsf, an allocation
engine that is both more space efficient and time-bounded, especially
for allocation sizes between PAGE_SIZE/2 and PAGE_SIZE.

The file xmalloc.c is deprecated but not yet deleted.  A simple
changein common/Makefile will change back to the legacy xmalloc/xfree
if needed for testing.

Code adapted from Nitin Gupta's tlsf-kmod, rev 229, found here:
http://code.google.com/p/compcache/source/browse/trunk/sub-projects/allocat=
ors/tlsf-kmod
with description and performance details here:
http://code.google.com/p/compcache/wiki/TLSFAllocator
(new Xen code uses 4K=3DPAGE_SIZE for the region size)

For detailed info on tlsf, see:
http://rtportal.upv.es/rtmalloc/

Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
---
 xen/common/Makefile       |    2 
 xen/common/xmalloc_tlsf.c |  655 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 656 insertions(+), 1 deletion(-)

diff -r 98ff908a91b7 -r 48fba1dbcfaf xen/common/Makefile
--- a/xen/common/Makefile       Thu Oct 16 09:52:40 2008 +0100
+++ b/xen/common/Makefile       Thu Oct 16 11:09:50 2008 +0100
@@ -25,7 +25,7 @@ obj-y += trace.o
 obj-y += trace.o
 obj-y += version.o
 obj-y += vsprintf.o
-obj-y += xmalloc.o
+obj-y += xmalloc_tlsf.o
 obj-y += rcupdate.o
 
 obj-$(perfc)       += perfc.o
diff -r 98ff908a91b7 -r 48fba1dbcfaf xen/common/xmalloc_tlsf.c
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/xen/common/xmalloc_tlsf.c Thu Oct 16 11:09:50 2008 +0100
@@ -0,0 +1,655 @@
+/*
+ * Two Levels Segregate Fit memory allocator (TLSF)
+ * Version 2.3.2
+ *
+ * Written by Miguel Masmano Tello <mimastel@xxxxxxxxxxxxx>
+ *
+ * Thanks to Ismael Ripoll for his suggestions and reviews
+ *
+ * Copyright (C) 2007, 2006, 2005, 2004
+ *
+ * This code is released using a dual license strategy: GPL/LGPL
+ * You can choose the licence that better fits your requirements.
+ *
+ * Released under the terms of the GNU General Public License Version 2.0
+ * Released under the terms of the GNU Lesser General Public License 
+ * Version 2.1
+ *
+ * This is kernel port of TLSF allocator.
+ * Original code can be found at: http://rtportal.upv.es/rtmalloc/
+ * Adapted for Linux by Nitin Gupta (nitingupta910@xxxxxxxxx)
+ * (http://code.google.com/p/compcache/source/browse/trunk/sub-projects
+ *  /allocators/tlsf-kmod r229 dated Aug 27, 2008
+ * Adapted for Xen by Dan Magenheimer (dan.magenheimer@xxxxxxxxxx)
+ */
+
+#include <xen/config.h>
+#include <xen/irq.h>
+#include <xen/mm.h>
+#include <asm/time.h>
+
+#define MAX_POOL_NAME_LEN       16
+
+typedef void *(get_memory)(size_t bytes);
+typedef void (put_memory)(void *ptr);
+
+/* Some IMPORTANT TLSF parameters */
+#define MEM_ALIGN       (sizeof(void *) * 2)
+#define MEM_ALIGN_MASK  (~(MEM_ALIGN - 1))
+
+#define MAX_FLI         (30)
+#define MAX_LOG2_SLI    (5)
+#define MAX_SLI         (1 << MAX_LOG2_SLI)
+
+#define FLI_OFFSET      (6)
+/* tlsf structure just will manage blocks bigger than 128 bytes */
+#define SMALL_BLOCK     (128)
+#define REAL_FLI        (MAX_FLI - FLI_OFFSET)
+#define MIN_BLOCK_SIZE  (sizeof(struct free_ptr))
+#define BHDR_OVERHEAD   (sizeof(struct bhdr) - MIN_BLOCK_SIZE)
+
+#define PTR_MASK        (sizeof(void *) - 1)
+#define BLOCK_SIZE_MASK (0xFFFFFFFF - PTR_MASK)
+
+#define GET_NEXT_BLOCK(addr, r) ((struct bhdr *) \
+                                ((char *)(addr) + (r)))
+#define ROUNDUP_SIZE(r)         (((r) + MEM_ALIGN - 1) & MEM_ALIGN_MASK)
+#define ROUNDDOWN_SIZE(r)       ((r) & MEM_ALIGN_MASK)
+#define ROUNDUP_PAGE(r)         (((r) + PAGE_SIZE - 1) & PAGE_MASK)
+
+#define BLOCK_STATE     (0x1)
+#define PREV_STATE      (0x2)
+
+/* bit 0 of the block size */
+#define FREE_BLOCK      (0x1)
+#define USED_BLOCK      (0x0)
+
+/* bit 1 of the block size */
+#define PREV_FREE       (0x2)
+#define PREV_USED       (0x0)
+
+static spinlock_t pool_list_lock;
+static struct list_head pool_list_head;
+
+struct free_ptr {
+    struct bhdr *prev;
+    struct bhdr *next;
+};
+
+struct bhdr {
+    /* All blocks in a region are linked in order of physical address */
+    struct bhdr *prev_hdr;
+    /*
+     * The size is stored in bytes
+     *  bit 0: block is free, if set
+     *  bit 1: previous block is free, if set
+     */
+    u32 size;
+    /* Free blocks in individual freelists are linked */
+    union {
+        struct free_ptr free_ptr;
+        u8 buffer[sizeof(struct free_ptr)];
+    } ptr;
+};
+
+struct pool {
+    /* First level bitmap (REAL_FLI bits) */
+    u32 fl_bitmap;
+
+    /* Second level bitmap */
+    u32 sl_bitmap[REAL_FLI];
+
+    /* Free lists */
+    struct bhdr *matrix[REAL_FLI][MAX_SLI];
+
+    spinlock_t lock;
+
+    size_t init_size;
+    size_t max_size;
+    size_t grow_size;
+
+    /* Basic stats */
+    size_t used_size;
+    size_t num_regions;
+
+    /* User provided functions for expanding/shrinking pool */
+    get_memory *get_mem;
+    put_memory *put_mem;
+
+    struct list_head list;
+
+    void *init_region;
+    char name[MAX_POOL_NAME_LEN];
+};
+
+/*
+ * Helping functions
+ */
+
+/**
+ * Returns indexes (fl, sl) of the list used to serve request of size r
+ */
+static inline void MAPPING_SEARCH(size_t *r, int *fl, int *sl)
+{
+    int t;
+
+    if ( *r < SMALL_BLOCK )
+    {
+        *fl = 0;
+        *sl = *r / (SMALL_BLOCK / MAX_SLI);
+    }
+    else
+    {
+        t = (1 << (fls(*r) - 1 - MAX_LOG2_SLI)) - 1;
+        *r = *r + t;
+        *fl = fls(*r) - 1;
+        *sl = (*r >> (*fl - MAX_LOG2_SLI)) - MAX_SLI;
+        *fl -= FLI_OFFSET;
+        /*if ((*fl -= FLI_OFFSET) < 0) // FL will be always >0!
+         *fl = *sl = 0;
+         */
+        *r &= ~t;
+    }
+}
+
+/**
+ * Returns indexes (fl, sl) which is used as starting point to search
+ * for a block of size r. It also rounds up requested size(r) to the
+ * next list.
+ */
+static inline void MAPPING_INSERT(size_t r, int *fl, int *sl)
+{
+    if ( r < SMALL_BLOCK )
+    {
+        *fl = 0;
+        *sl = r / (SMALL_BLOCK / MAX_SLI);
+    }
+    else
+    {
+        *fl = fls(r) - 1;
+        *sl = (r >> (*fl - MAX_LOG2_SLI)) - MAX_SLI;
+        *fl -= FLI_OFFSET;
+    }
+}
+
+/**
+ * Returns first block from a list that hold blocks larger than or
+ * equal to the one pointed by the indexes (fl, sl)
+ */
+static inline struct bhdr *FIND_SUITABLE_BLOCK(struct pool *p, int *fl,
+                                               int *sl)
+{
+    u32 tmp = p->sl_bitmap[*fl] & (~0 << *sl);
+    struct bhdr *b = NULL;
+
+    if ( tmp )
+    {
+        *sl = ffs(tmp) - 1;
+        b = p->matrix[*fl][*sl];
+    }
+    else
+    {
+        *fl = ffs(p->fl_bitmap & (~0 << (*fl + 1))) - 1;
+        if ( likely(*fl > 0) )
+        {
+            *sl = ffs(p->sl_bitmap[*fl]) - 1;
+            b = p->matrix[*fl][*sl];
+        }
+    }
+
+    return b;
+}
+
+/**
+ * Remove first free block(b) from free list with indexes (fl, sl).
+ */
+static inline void EXTRACT_BLOCK_HDR(struct bhdr *b, struct pool *p, int fl,
+                                     int sl)
+{
+    p->matrix[fl][sl] = b->ptr.free_ptr.next;
+    if ( p->matrix[fl][sl] )
+    {
+        p->matrix[fl][sl]->ptr.free_ptr.prev = NULL;
+    }
+    else
+    {
+        clear_bit(sl, &p->sl_bitmap[fl]);
+        if ( !p->sl_bitmap[fl] )
+            clear_bit(fl, &p->fl_bitmap);
+    }
+    b->ptr.free_ptr = (struct free_ptr) {NULL, NULL};
+}
+
+/**
+ * Removes block(b) from free list with indexes (fl, sl)
+ */
+static inline void EXTRACT_BLOCK(struct bhdr *b, struct pool *p, int fl,
+                                 int sl)
+{
+    if ( b->ptr.free_ptr.next )
+        b->ptr.free_ptr.next->ptr.free_ptr.prev =
+            b->ptr.free_ptr.prev;
+    if ( b->ptr.free_ptr.prev )
+        b->ptr.free_ptr.prev->ptr.free_ptr.next =
+            b->ptr.free_ptr.next;
+    if ( p->matrix[fl][sl] == b )
+    {
+        p->matrix[fl][sl] = b->ptr.free_ptr.next;
+        if ( !p->matrix[fl][sl] )
+        {
+            clear_bit(sl, &p->sl_bitmap[fl]);
+            if ( !p->sl_bitmap[fl] )
+                clear_bit (fl, &p->fl_bitmap);
+        }
+    }
+    b->ptr.free_ptr = (struct free_ptr) {NULL, NULL};
+}
+
+/**
+ * Insert block(b) in free list with indexes (fl, sl)
+ */
+static inline void INSERT_BLOCK(struct bhdr *b, struct pool *p, int fl, int sl)
+{
+    b->ptr.free_ptr = (struct free_ptr) {NULL, p->matrix[fl][sl]};
+    if ( p->matrix[fl][sl] )
+        p->matrix[fl][sl]->ptr.free_ptr.prev = b;
+    p->matrix[fl][sl] = b;
+    set_bit(sl, &p->sl_bitmap[fl]);
+    set_bit(fl, &p->fl_bitmap);
+}
+
+/**
+ * Region is a virtually contiguous memory region and Pool is
+ * collection of such regions
+ */
+static inline void ADD_REGION(void *region, size_t region_size,
+                              struct pool *pool)
+{
+    int fl, sl;
+    struct bhdr *b, *lb;
+
+    b = (struct bhdr *)(region);
+    b->prev_hdr = NULL;
+    b->size = ROUNDDOWN_SIZE(region_size - 2 * BHDR_OVERHEAD)
+        | FREE_BLOCK | PREV_USED;
+    MAPPING_INSERT(b->size & BLOCK_SIZE_MASK, &fl, &sl);
+    INSERT_BLOCK(b, pool, fl, sl);
+    /* The sentinel block: allows us to know when we're in the last block */
+    lb = GET_NEXT_BLOCK(b->ptr.buffer, b->size & BLOCK_SIZE_MASK);
+    lb->prev_hdr = b;
+    lb->size = 0 | USED_BLOCK | PREV_FREE;
+    pool->used_size += BHDR_OVERHEAD; /* only sentinel block is "used" */
+    pool->num_regions++;
+}
+
+/*
+ * Allocator code start
+ */
+
+/**
+ * tlsf_create_memory_pool - create dynamic memory pool
+ * @name: name of the pool
+ * @get_mem: callback function used to expand pool
+ * @put_mem: callback function used to shrink pool
+ * @init_size: inital pool size (in bytes)
+ * @max_size: maximum pool size (in bytes) - set this as 0 for no limit
+ * @grow_size: amount of memory (in bytes) added to pool whenever required
+ *
+ * All size values are rounded up to next page boundary.
+ */
+static void *tlsf_create_memory_pool(const char *name,
+                                     get_memory get_mem,
+                                     put_memory put_mem,
+                                     size_t init_size,
+                                     size_t max_size,
+                                     size_t grow_size)
+{
+    struct pool *pool;
+    void *region;
+    int pool_bytes, pool_order;
+
+    BUG_ON(max_size && (max_size < init_size));
+
+    pool_bytes = ROUNDUP_SIZE(sizeof(*pool));
+    pool_order = get_order_from_bytes(pool_bytes);
+
+    pool = (void *)alloc_xenheap_pages(pool_order);
+    if ( pool == NULL )
+        return NULL;
+    memset(pool, 0, pool_bytes);
+
+    /* Round to next page boundary */
+    init_size = ROUNDUP_PAGE(init_size);
+    max_size = ROUNDUP_PAGE(max_size);
+    grow_size = ROUNDUP_PAGE(grow_size);
+
+    /* pool global overhead not included in used size */
+    pool->used_size = 0;
+
+    pool->init_size = init_size;
+    pool->max_size = max_size;
+    pool->grow_size = grow_size;
+    pool->get_mem = get_mem;
+    pool->put_mem = put_mem;
+    pool->name[0] = '\0';  /* ignore name for now */
+    region = get_mem(init_size);
+    if ( region == NULL )
+        goto out_region;
+    ADD_REGION(region, init_size, pool);
+    pool->init_region = region;
+
+    spin_lock_init(&pool->lock);
+
+    spin_lock(&pool_list_lock);
+    list_add_tail(&pool->list, &pool_list_head);
+    spin_unlock(&pool_list_lock);
+
+    return pool;
+
+ out_region:
+    free_xenheap_pages(pool, pool_order);
+    return NULL;
+}
+
+#if 0
+
+/**
+ * tlsf_get_used_size - get memory currently used by given pool
+ *
+ * Used memory includes stored data + metadata + internal fragmentation
+ */
+static size_t tlsf_get_used_size(void *mem_pool)
+{
+    struct pool *pool = (struct pool *)mem_pool;
+    return pool->used_size;
+}
+
+/**
+ * tlsf_get_total_size - get total memory currently allocated for given pool
+ *
+ * This is the total memory currently allocated for this pool which includes
+ * used size + free size.
+ *
+ * (Total - Used) is good indicator of memory efficiency of allocator.
+ */
+static size_t tlsf_get_total_size(void *mem_pool)
+{
+    size_t total;
+    struct pool *pool = (struct pool *)mem_pool;
+    total = ROUNDUP_SIZE(sizeof(*pool))
+        + pool->init_size
+        + (pool->num_regions - 1) * pool->grow_size;
+    return total;
+}
+
+/**
+ * tlsf_destroy_memory_pool - cleanup given pool
+ * @mem_pool: Pool to be destroyed
+ *
+ * Data structures associated with pool are freed.
+ * All memory allocated from pool must be freed before
+ * destorying it.
+ */
+static void tlsf_destroy_memory_pool(void *mem_pool) 
+{
+    struct pool *pool;
+
+    if ( mem_pool == NULL )
+        return;
+
+    pool = (struct pool *)mem_pool;
+
+    /* User is destroying without ever allocating from this pool */
+    if ( tlsf_get_used_size(pool) == BHDR_OVERHEAD )
+    {
+        pool->put_mem(pool->init_region);
+        pool->used_size -= BHDR_OVERHEAD;
+    }
+
+    /* Check for memory leaks in this pool */
+    if ( tlsf_get_used_size(pool) )
+        printk("memory leak in pool: %s (%p). "
+               "%lu bytes still in use.\n",
+               pool->name, pool, (long)tlsf_get_used_size(pool));
+
+    spin_lock(&pool_list_lock);
+    list_del_init(&pool->list);
+    spin_unlock(&pool_list_lock);
+    pool->put_mem(pool);
+}
+
+#endif
+
+/**
+ * tlsf_malloc - allocate memory from given pool
+ * @size: no. of bytes
+ * @mem_pool: pool to allocate from
+ */
+static void *tlsf_malloc(size_t size, void *mem_pool)
+{
+    struct pool *pool = (struct pool *)mem_pool;
+    struct bhdr *b, *b2, *next_b, *region;
+    int fl, sl;
+    size_t tmp_size;
+
+    size = (size < MIN_BLOCK_SIZE) ? MIN_BLOCK_SIZE : ROUNDUP_SIZE(size);
+    /* Rounding up the requested size and calculating fl and sl */
+
+    spin_lock(&pool->lock);
+ retry_find:
+    MAPPING_SEARCH(&size, &fl, &sl);
+
+    /* Searching a free block */
+    if ( !(b = FIND_SUITABLE_BLOCK(pool, &fl, &sl)) )
+    {
+        /* Not found */
+        if ( size > (pool->grow_size - 2 * BHDR_OVERHEAD) )
+            goto out_locked;
+        if ( pool->max_size && (pool->init_size +
+                                pool->num_regions * pool->grow_size
+                                > pool->max_size) )
+            goto out_locked;
+        spin_unlock(&pool->lock);
+        if ( (region = pool->get_mem(pool->grow_size)) == NULL )
+            goto out;
+        spin_lock(&pool->lock);
+        ADD_REGION(region, pool->grow_size, pool);
+        goto retry_find;
+    }
+    EXTRACT_BLOCK_HDR(b, pool, fl, sl);
+
+    /*-- found: */
+    next_b = GET_NEXT_BLOCK(b->ptr.buffer, b->size & BLOCK_SIZE_MASK);
+    /* Should the block be split? */
+    tmp_size = (b->size & BLOCK_SIZE_MASK) - size;
+    if ( tmp_size >= sizeof(struct bhdr) )
+    {
+        tmp_size -= BHDR_OVERHEAD;
+        b2 = GET_NEXT_BLOCK(b->ptr.buffer, size);
+
+        b2->size = tmp_size | FREE_BLOCK | PREV_USED;
+        b2->prev_hdr = b;
+
+        next_b->prev_hdr = b2;
+
+        MAPPING_INSERT(tmp_size, &fl, &sl);
+        INSERT_BLOCK(b2, pool, fl, sl);
+
+        b->size = size | (b->size & PREV_STATE);
+    }
+    else
+    {
+        next_b->size &= (~PREV_FREE);
+        b->size &= (~FREE_BLOCK); /* Now it's used */
+    }
+
+    pool->used_size += (b->size & BLOCK_SIZE_MASK) + BHDR_OVERHEAD;
+
+    spin_unlock(&pool->lock);
+    return (void *)b->ptr.buffer;
+
+    /* Failed alloc */
+ out_locked:
+    spin_unlock(&pool->lock);
+
+ out:
+    return NULL;
+}
+
+/**
+ * tlsf_free - free memory from given pool
+ * @ptr: address of memory to be freed
+ * @mem_pool: pool to free from
+ */
+static void tlsf_free(void *ptr, void *mem_pool)
+{
+    struct pool *pool = (struct pool *)mem_pool;
+    struct bhdr *b, *tmp_b;
+    int fl = 0, sl = 0;
+
+    if ( unlikely(ptr == NULL) )
+        return;
+
+    b = (struct bhdr *)((char *) ptr - BHDR_OVERHEAD);
+
+    spin_lock(&pool->lock);
+    b->size |= FREE_BLOCK;
+    pool->used_size -= (b->size & BLOCK_SIZE_MASK) + BHDR_OVERHEAD;
+    b->ptr.free_ptr = (struct free_ptr) { NULL, NULL};
+    tmp_b = GET_NEXT_BLOCK(b->ptr.buffer, b->size & BLOCK_SIZE_MASK);
+    if ( tmp_b->size & FREE_BLOCK )
+    {
+        MAPPING_INSERT(tmp_b->size & BLOCK_SIZE_MASK, &fl, &sl);
+        EXTRACT_BLOCK(tmp_b, pool, fl, sl);
+        b->size += (tmp_b->size & BLOCK_SIZE_MASK) + BHDR_OVERHEAD;
+    }
+    if ( b->size & PREV_FREE )
+    {
+        tmp_b = b->prev_hdr;
+        MAPPING_INSERT(tmp_b->size & BLOCK_SIZE_MASK, &fl, &sl);
+        EXTRACT_BLOCK(tmp_b, pool, fl, sl);
+        tmp_b->size += (b->size & BLOCK_SIZE_MASK) + BHDR_OVERHEAD;
+        b = tmp_b;
+    }
+    tmp_b = GET_NEXT_BLOCK(b->ptr.buffer, b->size & BLOCK_SIZE_MASK);
+    tmp_b->prev_hdr = b;
+
+    MAPPING_INSERT(b->size & BLOCK_SIZE_MASK, &fl, &sl);
+
+    if ( (b->prev_hdr == NULL) && ((tmp_b->size & BLOCK_SIZE_MASK) == 0) )
+    {
+        pool->put_mem(b);
+        pool->num_regions--;
+        pool->used_size -= BHDR_OVERHEAD; /* sentinel block header */
+        goto out;
+    }
+
+    INSERT_BLOCK(b, pool, fl, sl);
+
+    tmp_b->size |= PREV_FREE;
+    tmp_b->prev_hdr = b;
+ out:
+    spin_unlock(&pool->lock);
+}
+
+/*
+ * Glue for xmalloc().
+ */
+
+static struct pool *xenpool;
+
+static void *tlsf_get_xenheap_page(size_t size)
+{
+    ASSERT(size == PAGE_SIZE);
+    return alloc_xenheap_pages(0);
+}
+
+static void tlsf_put_xenheap_page(void *p)
+{
+    free_xenheap_pages(p,0);
+}
+
+static void *tlsf_xenheap_malloc_whole_pages(size_t size)
+{
+    struct bhdr *b;
+    unsigned int pageorder = get_order_from_bytes(size + BHDR_OVERHEAD);
+
+    b = alloc_xenheap_pages(pageorder);
+    if ( b == NULL )
+        return NULL;
+
+    b->size = (1 << (pageorder + PAGE_SHIFT));
+    return (void *)b->ptr.buffer;
+}
+
+static void tlsf_xenheap_init(void)
+{
+    INIT_LIST_HEAD(&pool_list_head);
+    spin_lock_init(&pool_list_lock);
+    xenpool = tlsf_create_memory_pool(
+        "", tlsf_get_xenheap_page,
+        tlsf_put_xenheap_page, PAGE_SIZE, 0, PAGE_SIZE);
+    BUG_ON(!xenpool);
+}
+
+/*
+ * xmalloc()
+ */
+
+void *_xmalloc(size_t size, size_t align)
+{
+    void *p;
+    u32 pad;
+
+    ASSERT(!in_irq());
+
+    ASSERT((align & (align - 1)) == 0);
+    if ( align < MEM_ALIGN )
+        align = MEM_ALIGN;
+    size += align - MEM_ALIGN;
+
+    if ( !xenpool )
+        tlsf_xenheap_init();
+
+    if ( size >= (PAGE_SIZE - (2*BHDR_OVERHEAD)) )
+        p = tlsf_xenheap_malloc_whole_pages(size);
+    else
+        p = tlsf_malloc(size, xenpool);
+
+    /* Add alignment padding. */
+    if ( (pad = -(long)p & (align - 1)) != 0 )
+    {
+        char *q = (char *)p + pad;
+        struct bhdr *b = (struct bhdr *)(q - BHDR_OVERHEAD);
+        ASSERT(q > (char *)p);
+        b->size = pad | 1;
+        p = q;
+    }
+
+    ASSERT(((unsigned long)p & (align - 1)) == 0);
+    return p;
+}
+
+void xfree(void *p)
+{
+    struct bhdr *b;
+
+    ASSERT(!in_irq());
+
+    if ( p == NULL )
+        return;
+
+    /* Strip alignment padding. */
+    b = (struct bhdr *)((char *) p - BHDR_OVERHEAD);
+    if ( b->size & 1 )
+    {
+        p = (char *)p - (b->size & ~1u);
+        b = (struct bhdr *)((char *)p - BHDR_OVERHEAD);
+        ASSERT(!(b->size & 1));
+    }
+
+    if ( b->size >= (PAGE_SIZE - (2*BHDR_OVERHEAD)) )
+        free_xenheap_pages((void *)b, get_order_from_bytes(b->size));
+    else
+        tlsf_free(p, xenpool);
+}

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