[Qemu-devel] [PATCH 3/4] libqos: add a simple first-fit memory allocator

[John Snow <jsnow@redhat.com>]

Implement a simple first-fit memory allocator that
attempts to keep track of leased blocks of memory
in order to be able to re-use blocks.

Additionally, allow the user to specify when
initializing the device that upon cleanup,
we would like to assert that there are no
blocks in use. This may be useful for identifying
problems in qtests that use more complicated
set-up and tear-down routines.

This functionality is used in my upcoming ahci-test v2
patch set, but I didn't see fit to enable it for any
existing tests, which will continue to operate the
same as they have prior.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 tests/libqos/malloc-pc.c | 321 +++++++++++++++++++++++++++++++++++++++++++++--
 tests/libqos/malloc-pc.h |   9 ++
 2 files changed, 321 insertions(+), 9 deletions(-)

diff --git a/tests/libqos/malloc-pc.c b/tests/libqos/malloc-pc.c
index 2efd095..410181d 100644
--- a/tests/libqos/malloc-pc.c
+++ b/tests/libqos/malloc-pc.c
@@ -21,41 +21,336 @@
 
 #define PAGE_SIZE (4096)
 
+typedef struct mem_block {
+    struct mem_block *prev;
+    struct mem_block *next;
+    uint64_t size;
+    uint64_t addr;
+} MemBlock;
+typedef MemBlock MemList;
+
 typedef struct PCAlloc
 {
     QGuestAllocator alloc;
-
+    PCAllocOpts opts;
     uint64_t start;
     uint64_t end;
+
+    MemList used;
+    MemList free;
 } PCAlloc;
 
-static uint64_t pc_alloc(QGuestAllocator *allocator, size_t size)
+/** Generic List Management **/
+
+static void mlist_header_init(MemBlock *header, MemBlock *head)
+{
+    header->prev = NULL;
+    header->next = head;
+    header->size = 0;
+    header->addr = 0;
+
+    if (head) {
+        head->prev = header;
+    }
+}
+
+static MemBlock *mlist_new(uint64_t addr, uint64_t size)
+{
+    MemBlock *block = g_malloc(sizeof(MemBlock));
+
+    if (!size) {
+        return NULL;
+    }
+
+    block->prev = NULL;
+    block->next = NULL;
+    block->addr = addr;
+    block->size = size;
+
+    return block;
+}
+
+static MemBlock *mlist_find_key(MemList *head, uint64_t addr)
+{
+    MemBlock *node = head;
+    while ((node = node->next)) {
+        if (node->addr == addr) {
+            return node;
+        }
+    }
+    return NULL;
+}
+
+static MemBlock *mlist_find_space(MemList *head, uint64_t size)
+{
+    MemBlock *node = head;
+    while ((node = node->next)) {
+        if (node->size >= size) {
+            return node;
+        }
+    }
+    return NULL;
+}
+
+static MemBlock *mlist_insert(MemBlock *node, MemBlock *insr)
+{
+    g_assert_null(insr->next);
+    g_assert_null(insr->prev);
+
+    insr->next = node;
+    insr->prev = node->prev;
+
+    node->prev = insr;
+    insr->prev->next = insr;
+
+    return insr;
+}
+
+static MemBlock *mlist_append(MemBlock *node, MemBlock *insr)
+{
+    g_assert(node);
+
+    for ( ; node->next; node = node->next) {
+        /* nihil */
+    }
+
+    node->next = insr;
+    insr->next = NULL;
+    insr->prev = node;
+
+    return insr;
+}
+
+static MemBlock *mlist_unlink(MemBlock *node)
+{
+    MemBlock *left, *right;
+    g_assert(node);
+
+    left = node->prev;
+    right = node->next;
+
+    g_assert(left);
+    left->next = right;
+
+    if (right) {
+        right->prev = left;
+    }
+
+    node->prev = NULL;
+    node->next = NULL;
+
+    return node;
+}
+
+static void mlist_delete(MemBlock *node)
+{
+    g_assert(node);
+
+    mlist_unlink(node);
+    g_free(node);
+}
+
+static MemBlock *mlist_sort_insert(MemList *head, MemBlock *insr)
+{
+    MemBlock *node = head;
+    g_assert(head);
+    g_assert(insr);
+
+    while ((node = node->next)) {
+        if (insr->addr < node->addr) {
+            return mlist_insert(node, insr);
+        }
+    }
+
+    return mlist_append(head, insr);
+}
+
+/** Implementation-Based List Routines **/
+
+static inline uint64_t mlist_boundary(MemBlock *node)
+{
+    return node->size + node->addr;
+}
+
+static MemBlock *mlist_join(MemBlock *left, MemBlock *right)
+{
+    g_assert(left && right);
+
+    left->size += right->size;
+    mlist_delete(right);
+    return left;
+}
+
+static void mlist_coalesce(MemBlock *node)
+{
+    g_assert(node);
+    MemBlock *left;
+    MemBlock *right;
+    char merge;
+
+    do {
+        merge = 0;
+        left = node->prev;
+        right = node->next;
+
+        /* clowns to the left of me */
+        if (left && mlist_boundary(left) == node->addr) {
+            node = mlist_join(left, node);
+            merge = 1;
+        }
+
+        /* jokers to the right */
+        if (right && mlist_boundary(node) == right->addr) {
+            node = mlist_join(node, right);
+            merge = 1;
+        }
+
+    } while (merge);
+}
+
+static uint64_t pc_mlist_fulfill(PCAlloc *s, MemBlock *freenode, uint64_t size)
 {
-    PCAlloc *s = container_of(allocator, PCAlloc, alloc);
     uint64_t addr;
+    MemBlock *usednode;
 
+    g_assert(freenode);
+    g_assert_cmpint(freenode->size, >=, size);
 
-    size += (PAGE_SIZE - 1);
-    size &= -PAGE_SIZE;
+    addr = freenode->addr;
+    freenode->addr += size;
+    freenode->size -= size;
 
-    g_assert_cmpint((s->start + size), <=, s->end);
+    if (freenode->size == 0) {
+        mlist_delete(freenode);
+    }
 
-    addr = s->start;
-    s->start += size;
+    usednode = mlist_new(addr, size);
+    mlist_sort_insert(&s->used, usednode);
 
     return addr;
 }
 
+/* To assert the correctness of the list.
+ * Used only if PC_ALLOC_PARANOID is set. */
+static void pc_mlist_check(PCAlloc *s)
+{
+    MemBlock *node = &(s->free);
+    uint64_t addr = 0;
+    uint64_t next = 0;
+
+    while ((node = node->next)) {
+        g_assert_cmpint(node->addr, >, addr);
+        g_assert_cmpint(node->addr, >=, next);
+        addr = node->addr;
+        next = node->addr + node->size;
+    }
+
+    node = &(s->used);
+    addr = 0;
+    next = 0;
+    while ((node = node->next)) {
+        g_assert_cmpint(node->addr, >, addr);
+        g_assert_cmpint(node->addr, >=, next);
+        addr = node->addr;
+        next = node->addr + node->size;
+    }
+}
+
+static uint64_t pc_mlist_alloc(PCAlloc *s, uint64_t size)
+{
+    MemBlock *node;
+
+    node = mlist_find_space(&s->free, size);
+    if (!node) {
+        fprintf(stderr, "Out of guest memory.\n");
+        g_assert_not_reached();
+    }
+    return pc_mlist_fulfill(s, node, size);
+}
+
+static void pc_mlist_free(PCAlloc *s, uint64_t addr)
+{
+    MemBlock *node;
+
+    node = mlist_find_key(&s->used, addr);
+    if (!node) {
+        fprintf(stderr, "Error: no record found for 0x%016lx allocation\n",
+                addr);
+        g_assert_not_reached();
+    }
+
+    /* Rip it out of the used list and re-insert back into the free list. */
+    mlist_unlink(node);
+    mlist_sort_insert(&s->free, node);
+    mlist_coalesce(node);
+}
+
+static uint64_t pc_alloc(QGuestAllocator *allocator, size_t size)
+{
+    PCAlloc *s = container_of(allocator, PCAlloc, alloc);
+    uint64_t rsize = size;
+    uint64_t naddr;
+
+    rsize += (PAGE_SIZE - 1);
+    rsize &= -PAGE_SIZE;
+    g_assert_cmpint((s->start + rsize), <=, s->end);
+    g_assert_cmpint(rsize, >=, size);
+
+    naddr = pc_mlist_alloc(s, rsize);
+    if (s->opts & PC_ALLOC_PARANOID) {
+        pc_mlist_check(s);
+    }
+
+    return naddr;
+}
+
 static void pc_free(QGuestAllocator *allocator, uint64_t addr)
 {
+    PCAlloc *s = container_of(allocator, PCAlloc, alloc);
+
+    pc_mlist_free(s, addr);
+    if (s->opts & PC_ALLOC_PARANOID) {
+        pc_mlist_check(s);
+    }
+}
+
+/*
+ * Mostly for valgrind happiness, but it does offer
+ * a chokepoint for debugging guest memory leaks, too.
+ */
+void pc_alloc_uninit(QGuestAllocator *allocator)
+{
+    PCAlloc *s = container_of(allocator, PCAlloc, alloc);
+    MemBlock *node;
+    MemBlock *tmp;
+
+    for (node = s->used.next; node; node = tmp) {
+        if (s->opts & (PC_ALLOC_LEAK_WARN | PC_ALLOC_LEAK_ASSERT)) {
+            fprintf(stderr, "guest malloc leak @ 0x%016lx size 0x%016lx\n",
+                    node->addr, node->size);
+        }
+        if (s->opts & PC_ALLOC_LEAK_ASSERT) {
+            g_assert_not_reached();
+        }
+        tmp = node->next;
+        g_free(node);
+    }
+
+    for (node = s->free.next; node; node = tmp) {
+        tmp = node->next;
+        g_free(node);
+    }
+
+    g_free(s);
 }
 
-QGuestAllocator *pc_alloc_init(void)
+QGuestAllocator *pc_alloc_init_flags(PCAllocOpts flags)
 {
     PCAlloc *s = g_malloc0(sizeof(*s));
     uint64_t ram_size;
     QFWCFG *fw_cfg = pc_fw_cfg_init();
 
+    s->opts = flags;
     s->alloc.alloc = pc_alloc;
     s->alloc.free = pc_free;
 
@@ -67,5 +362,13 @@ QGuestAllocator *pc_alloc_init(void)
     /* Respect PCI hole */
     s->end = MIN(ram_size, 0xE0000000);
 
+    mlist_header_init(&s->used, NULL);
+    mlist_header_init(&s->free, mlist_new(s->start, s->end));
+
     return &s->alloc;
 }
+
+inline QGuestAllocator *pc_alloc_init(void)
+{
+    return pc_alloc_init_flags(PC_ALLOC_NO_FLAGS);
+}
diff --git a/tests/libqos/malloc-pc.h b/tests/libqos/malloc-pc.h
index ff964ab..9f525e3 100644
--- a/tests/libqos/malloc-pc.h
+++ b/tests/libqos/malloc-pc.h
@@ -15,6 +15,15 @@
 
 #include "libqos/malloc.h"
 
+typedef enum {
+    PC_ALLOC_NO_FLAGS    = 0x00,
+    PC_ALLOC_LEAK_WARN   = 0x01,
+    PC_ALLOC_LEAK_ASSERT = 0x02,
+    PC_ALLOC_PARANOID    = 0x04
+} PCAllocOpts;
+
 QGuestAllocator *pc_alloc_init(void);
+QGuestAllocator *pc_alloc_init_flags(PCAllocOpts flags);
+void             pc_alloc_uninit(QGuestAllocator *allocator);
 
 #endif
-- 
1.9.3