sub-page allocations work, still some FIXMEs to go.

alloc/alloc.c

@@ -19,76 +19,160 @@
 /* FIXME: Reduce. */
 #define MIN_SIZE (getpagesize() * 2)
 
-/* Metadata looks like this:
- * <unsigned long metalen> <page states> <align-pad> [<1-byte-len> <free|bit|uniform> bits...]* [unsigned long next]. 
+/* What's the granularity of sub-page allocs? */
+#define BITMAP_GRANULARITY 4
+
+/* File layout:
+ *
+ *  file := pagestates pad metadata
+ *  pagestates := pages * 2-bits-per-page
+ *  pad := pad to next ALIGNOF(metadata)
+ *
+ *  metadata := metalen next-ptr metabits
+ *  metabits := freeblock | bitblock
+ *  freeblock := 0+
+ *  bitblock := 2-bits-per-bit-in-page 1
  */
+struct metaheader
+{
+	/* Length (after this header).  (FIXME: Could be in pages). */
+	unsigned long metalen;
+	/* Next meta header, or 0 */
+	unsigned long next;
+	/* Bits start here. */
+};
 
 #define BITS_PER_PAGE 2
+/* FIXME: Don't use page states for bitblock.  It's tacky and confusing. */
 enum page_state
 {
 	FREE,
 	TAKEN,
 	TAKEN_START,
+	SUBPAGE,
 };
 
+/* Assumes a is a power of two. */
+static unsigned long align_up(unsigned long x, unsigned long a)
+{
+	return (x + a - 1) & ~(a - 1);
+}
+
+static unsigned long div_up(unsigned long x, unsigned long a)
+{
+	return (x + a - 1) / a;
+}
+
+/* The offset of metadata for a subpage allocation is found at the end
+ * of the subpage */
+#define SUBPAGE_METAOFF (getpagesize() - sizeof(unsigned long))
+
+/* This is the length of metadata in bits.  It consists of a TAKEN header,
+ * then two bits for every BITMAP_GRANULARITY of usable bytes in the. */
+#define BITMAP_METABITLEN						\
+    ((1 + div_up(SUBPAGE_METAOFF, BITMAP_GRANULARITY)) * BITS_PER_PAGE)
+
+/* This is the length in bytes. */
+#define BITMAP_METALEN (div_up(BITMAP_METABITLEN, CHAR_BIT))
+
 static enum page_state get_page_state(const uint8_t *bits, unsigned long page)
 {
-	bits += sizeof(unsigned long);
 	return bits[page * 2 / CHAR_BIT] >> (page * 2 % CHAR_BIT) & 3;
 }
 
 static void set_page_state(uint8_t *bits, unsigned long page, enum page_state s)
 {
-	bits += sizeof(unsigned long);
 	bits[page * 2 / CHAR_BIT] &= ~(3 << (page * 2 % CHAR_BIT));
 	bits[page * 2 / CHAR_BIT] |= ((uint8_t)s << (page * 2 % CHAR_BIT));
 }
 
-/* Assumes a is a power of two. */
-static unsigned long align_up(unsigned long x, unsigned long a)
+static struct metaheader *first_mheader(void *pool, unsigned long poolsize)
 {
-	return (x + a - 1) & ~(a - 1);
+	unsigned int pagestatelen;
+
+	pagestatelen = align_up(div_up(poolsize/getpagesize() * BITS_PER_PAGE,
+				       CHAR_BIT),
+				ALIGNOF(struct metaheader));
+	return (struct metaheader *)((char *)pool + pagestatelen);
 }
 
-static unsigned long div_up(unsigned long x, unsigned long a)
+static struct metaheader *next_mheader(void *pool, struct metaheader *mh)
 {
-	return (x + a - 1) / a;
+	if (!mh->next)
+		return NULL;
+
+	return (struct metaheader *)((char *)pool + mh->next);
 }
 
-static unsigned long metadata_length(void *pool, unsigned long poolsize)
+static unsigned long pool_offset(void *pool, void *p)
 {
-	return *(unsigned long *)pool;
+	return (char *)p - (char *)pool;
 }
 
 void alloc_init(void *pool, unsigned long poolsize)
 {
 	/* FIXME: Alignment assumptions about pool. */
-	unsigned long *metalen = pool, pages, pagestatebytes, i;
+	unsigned long len, i;
+	struct metaheader *mh;
 
 	if (poolsize < MIN_SIZE)
 		return;
 
-	pages = poolsize / getpagesize();
+	mh = first_mheader(pool, poolsize);
 
-	/* First comes the metadata length, then 2 bits per page, then
-	 * the next pointer. */
-	pagestatebytes = div_up(pages * BITS_PER_PAGE, CHAR_BIT);
-	*metalen = sizeof(*metalen)
-		+ align_up(pagestatebytes, ALIGNOF(unsigned long))
-		+ sizeof(unsigned long);
-
-	/* Mark all the bits FREE to start, and zero the next pointer. */
+	/* len covers all page states, plus the metaheader. */
+	len = (char *)(mh + 1) - (char *)pool;
+	/* Mark all page states FREE */
 	BUILD_ASSERT(FREE == 0);
-	memset(metalen + 1, 0, *metalen - sizeof(*metalen));
+	memset(pool, 0, len);
+
+	/* metaheader len takes us up to next page boundary. */
+	mh->metalen = align_up(len, getpagesize()) - len;
 
-	/* Mark the metadata page(s) allocated. */
+	/* Mark the pagestate and metadata page(s) allocated. */
 	set_page_state(pool, 0, TAKEN_START);
-	for (i = 1; i < div_up(*metalen, getpagesize()); i++)
+	for (i = 1; i < div_up(len, getpagesize()); i++)
 		set_page_state(pool, i, TAKEN);
 }
 
-static void *alloc_get_pages(void *pool, unsigned long poolsize,
-			     unsigned long pages, unsigned long align)
+/* Two bits per element, representing page states.  Returns 0 on fail. */
+static unsigned long alloc_from_bitmap(uint8_t *bits, unsigned long elems,
+				       unsigned long want, unsigned long align)
+{
+	long i;
+	unsigned long free;
+
+	free = 0;
+	/* We allocate from far end, to increase ability to expand metadata. */
+	for (i = elems - 1; i >= 0; i--) {
+		switch (get_page_state(bits, i)) {
+		case FREE:
+			if (++free >= want) {
+				unsigned long j;
+
+				/* They might ask for large alignment. */
+				if (align && i % align)
+					continue;
+
+				for (j = i+1; j < i + want; j++)
+					set_page_state(bits, j, TAKEN);
+				set_page_state(bits, i, TAKEN_START);
+				return i;
+			}
+			break;
+		case SUBPAGE:
+		case TAKEN_START:
+		case TAKEN:
+			free = 0;
+			break;
+		}
+	}
+
+	return 0;
+}
+
+static unsigned long alloc_get_pages(void *pool, unsigned long poolsize,
+				     unsigned long pages, unsigned long align)
 {
 	long i;
 	unsigned long free;
@@ -99,19 +183,21 @@ static void *alloc_get_pages(void *pool, unsigned long poolsize,
 		switch (get_page_state(pool, i)) {
 		case FREE:
 			if (++free >= pages) {
-				unsigned long j;
-				char *ret = (char *)pool + i * getpagesize();
+				unsigned long j, addr;
+
+				addr = (unsigned long)pool + i * getpagesize();
 
 				/* They might ask for multi-page alignment. */
-				if ((unsigned long)ret % align)
+				if (addr % align)
 					continue;
 
 				for (j = i+1; j < i + pages; j++)
 					set_page_state(pool, j, TAKEN);
 				set_page_state(pool, i, TAKEN_START);
-				return ret;
+				return i;
 			}
 			break;
+		case SUBPAGE:
 		case TAKEN_START:
 		case TAKEN:
 			free = 0;
@@ -119,88 +205,357 @@ static void *alloc_get_pages(void *pool, unsigned long poolsize,
 		}
 	}
 
+	return 0;
+}
+
+/* Offset to metadata is at end of page. */
+static unsigned long *metadata_off(void *pool, unsigned long page)
+{
+	return (unsigned long *)
+		((char *)pool + (page+1)*getpagesize() - sizeof(unsigned long));
+}
+
+static uint8_t *get_page_metadata(void *pool, unsigned long page)
+{
+	return (uint8_t *)pool + *metadata_off(pool, page);
+}
+
+static void set_page_metadata(void *pool, unsigned long page, uint8_t *meta)
+{
+	*metadata_off(pool, page) = meta - (uint8_t *)pool;
+}
+
+static void *sub_page_alloc(void *pool, unsigned long page,
+			    unsigned long size, unsigned long align)
+{
+	uint8_t *bits = get_page_metadata(pool, page);
+	unsigned long i;
+
+	/* TAKEN at end means a bitwise alloc. */
+	assert(get_page_state(bits, getpagesize()/BITMAP_GRANULARITY - 1)
+	       == TAKEN);
+
+	/* Our bits are the same as the page bits. */
+	i = alloc_from_bitmap(bits, getpagesize()/BITMAP_GRANULARITY,
+			      div_up(size, BITMAP_GRANULARITY),
+			      align / BITMAP_GRANULARITY);
+
+	/* Can't allocate? */
+	if (i == 0)
+		return NULL;
+
+	return (char *)pool + page*getpagesize() + i*BITMAP_GRANULARITY;
+}
+
+static uint8_t *alloc_metaspace(struct metaheader *mh, unsigned long bytes)
+{
+	uint8_t *meta = (uint8_t *)(mh + 1);
+	unsigned long free = 0, len;
+	long i;
+
+	/* TAKEN tags end a subpage alloc. */
+	for (i = mh->metalen * CHAR_BIT / BITS_PER_PAGE - 1; i >= 0; i -= len) {
+		switch (get_page_state(meta, i)) {
+		case FREE:
+			len = 1;
+			free++;
+			if (free == bytes * CHAR_BIT / BITS_PER_PAGE) {
+				/* TAKEN marks end of metablock. */
+				set_page_state(meta, i + free - 1, TAKEN);
+				return meta + i / (CHAR_BIT / BITS_PER_PAGE);
+			}
+			break;
+		case TAKEN:
+			/* Skip over this allocated part. */
+			len = BITMAP_METALEN * CHAR_BIT;
+			free = 0;
+			break;
+		default:
+			assert(0);
+			return NULL;
+		}
+	}
 	return NULL;
 }
 
+/* We need this many bytes of metadata. */
+static uint8_t *new_metadata(void *pool, unsigned long poolsize,
+			     unsigned long bytes)
+{
+	struct metaheader *mh, *newmh;
+	unsigned long page;
+
+	for (mh = first_mheader(pool,poolsize); mh; mh = next_mheader(pool,mh)){
+		uint8_t *meta = alloc_metaspace(mh, bytes);
+
+		if (meta)
+			return meta;
+	}
+
+	/* No room for metadata?  Can we expand an existing one? */
+	for (mh = first_mheader(pool,poolsize); mh; mh = next_mheader(pool,mh)){
+		/* It should end on a page boundary. */
+		unsigned long nextpage;
+
+		nextpage = pool_offset(pool, (char *)(mh + 1) + mh->metalen);
+		assert(nextpage % getpagesize() == 0);
+
+		/* Now, can we grab that page? */
+		if (get_page_state(pool, nextpage / getpagesize()) != FREE)
+			continue;
+
+		/* OK, expand metadata, do it again. */
+		set_page_state(pool, nextpage / getpagesize(), TAKEN);
+		memset((char *)pool + nextpage, 0, getpagesize());
+		mh->metalen += getpagesize();
+		return alloc_metaspace(mh, bytes);
+	}
+
+	/* No metadata left at all? */
+	page = alloc_get_pages(pool, poolsize, div_up(bytes, getpagesize()), 1);
+	if (!page)
+		return NULL;
+
+	newmh = (struct metaheader *)((char *)pool + page * getpagesize());
+	newmh->metalen = getpagesize() - sizeof(*mh);
+	memset(newmh + 1, 0, newmh->metalen);
+
+	/* Sew it into linked list */
+	mh = first_mheader(pool,poolsize);
+	newmh->next = mh->next;
+	mh->next = (char *)newmh - (char *)pool;
+
+	return alloc_metaspace(newmh, bytes);
+}
+
+static void alloc_free_pages(void *pool, unsigned long pagenum)
+{
+	assert(get_page_state(pool, pagenum) == TAKEN_START);
+	set_page_state(pool, pagenum, FREE);
+	while (get_page_state(pool, ++pagenum) == TAKEN)
+		set_page_state(pool, pagenum, FREE);
+}
+
+static void *alloc_sub_page(void *pool, unsigned long poolsize,
+			    unsigned long size, unsigned long align)
+{
+	unsigned long i;
+	uint8_t *metadata;
+
+	/* Look for partial page. */
+	for (i = 0; i < poolsize / getpagesize(); i++) {
+		void *ret;
+		if (get_page_state(pool, i) != SUBPAGE)
+			continue;
+
+		ret = sub_page_alloc(pool, i, size, align);
+		if (ret)
+			return ret;
+	}
+
+	/* Create new SUBPAGE page. */
+	i = alloc_get_pages(pool, poolsize, 1, 1);
+	if (i == 0)
+		return NULL;
+
+	/* Get metadata for page. */
+	metadata = new_metadata(pool, poolsize, BITMAP_METALEN);
+	if (!metadata) {
+		alloc_free_pages(pool, i);
+		return NULL;
+	}
+
+	/* Actually, this is a SUBPAGE page now. */
+	set_page_state(pool, i, SUBPAGE);
+
+	/* Set metadata pointer for page. */
+	set_page_metadata(pool, i, metadata);
+
+	/* Do allocation like normal */
+	return sub_page_alloc(pool, i, size, align);
+}
+
 void *alloc_get(void *pool, unsigned long poolsize,
 		unsigned long size, unsigned long align)
 {
 	if (poolsize < MIN_SIZE)
 		return NULL;
 
-	if (size >= getpagesize() || align > getpagesize()) {
-		unsigned long pages = (size + getpagesize()-1) / getpagesize();
-		return alloc_get_pages(pool, poolsize, pages, align);
+	/* Sub-page allocations have an overhead of 25%. */
+	if (size + size/4 >= getpagesize() || align >= getpagesize()) {
+		unsigned long ret, pages = div_up(size, getpagesize());
+
+		ret = alloc_get_pages(pool, poolsize, pages, align);
+		if (ret == 0)
+			return NULL;
+		return (char *)pool + ret * getpagesize();
 	}
 
-	/* FIXME: Sub-page allocations. */
-	return alloc_get_pages(pool, poolsize, 1, align);
+	return alloc_sub_page(pool, poolsize, size, align);
+}
+
+static void subpage_free(void *pool, unsigned long pagenum, void *free)
+{
+	unsigned long off = (unsigned long)free % getpagesize();
+	uint8_t *metadata;
+
+	assert(off < SUBPAGE_METAOFF);
+	assert(off % BITMAP_GRANULARITY == 0);
+
+	metadata = get_page_metadata(pool, pagenum);
+
+	off /= BITMAP_GRANULARITY;
+
+	set_page_state(metadata, off++, FREE);
+	while (off < SUBPAGE_METAOFF / BITMAP_GRANULARITY
+	       && get_page_state(metadata, off) == TAKEN)
+		set_page_state(metadata, off++, FREE);
+
+	/* FIXME: If whole page free, free page and metadata. */
 }
 
 void alloc_free(void *pool, unsigned long poolsize, void *free)
 {
-	unsigned long pagenum, metalen;
+	unsigned long pagenum;
+	struct metaheader *mh;
 
 	if (!free)
 		return;
 
 	assert(poolsize >= MIN_SIZE);
 
-	metalen = metadata_length(pool, poolsize);
-
-	assert((char *)free >= (char *)pool + metalen);
+	mh = first_mheader(pool, poolsize);
+	assert((char *)free >= (char *)(mh + 1) + mh->metalen);
 	assert((char *)pool + poolsize > (char *)free);
-	assert((unsigned long)free % getpagesize() == 0);
 
-	pagenum = ((char *)free - (char *)pool) / getpagesize();
+	pagenum = pool_offset(pool, free) / getpagesize();
 
-	assert(get_page_state(pool, pagenum) == TAKEN_START);
-	set_page_state(pool, pagenum, FREE);
-	while (get_page_state(pool, ++pagenum) == TAKEN)
-		set_page_state(pool, pagenum, FREE);
+	if (get_page_state(pool, pagenum) == SUBPAGE)
+		subpage_free(pool, pagenum, free);
+	else {
+		assert((unsigned long)free % getpagesize() == 0);
+		alloc_free_pages(pool, pagenum);
+	}
+}
+
+static bool is_metadata_page(void *pool, unsigned long poolsize,
+			     unsigned long page)
+{
+	struct metaheader *mh;
+
+	for (mh = first_mheader(pool,poolsize); mh; mh = next_mheader(pool,mh)){
+		unsigned long start, end;
+
+		start = pool_offset(pool, mh);
+		end = pool_offset(pool, (char *)(mh+1) + mh->metalen);
+		if (page >= start/getpagesize() && page < end/getpagesize())
+			return true;
+	}
+	return false;
+}
+
+static bool check_subpage(void *pool, unsigned long poolsize,
+			  unsigned long page)
+{
+	unsigned long *mhoff = metadata_off(pool, page);
+	unsigned int i;
+	enum page_state last_state = FREE;
+
+	if (*mhoff + sizeof(struct metaheader) > poolsize)
+		return false;
+
+	if (*mhoff % ALIGNOF(struct metaheader) != 0)
+		return false;
+
+	/* It must point to a metadata page. */
+	if (!is_metadata_page(pool, poolsize, *mhoff / getpagesize()))
+		return false;
+
+	/* Marker at end of subpage allocation is "taken" */
+	if (get_page_state((uint8_t *)pool + *mhoff,
+			   getpagesize()/BITMAP_GRANULARITY - 1) != TAKEN)
+		return false;
+
+	for (i = 0; i < SUBPAGE_METAOFF / BITMAP_GRANULARITY; i++) {
+		enum page_state state;
+
+		state = get_page_state((uint8_t *)pool + *mhoff, i);
+		switch (state) {
+		case SUBPAGE:
+			return false;
+		case TAKEN:
+			if (last_state == FREE)
+				return false;
+			break;
+		default:
+			break;
+		}
+		last_state = state;
+	}
+	return true;
 }
 
 bool alloc_check(void *pool, unsigned long poolsize)
 {
-	unsigned long i, metalen, pagestatebytes;
+	unsigned long i;
+	struct metaheader *mh;
 	enum page_state last_state = FREE;
+	bool was_metadata = false;
 
 	if (poolsize < MIN_SIZE)
 		return true;
 
-	metalen = metadata_length(pool, poolsize);
 	if (get_page_state(pool, 0) != TAKEN_START)
 		return false;
 
-	pagestatebytes = div_up(poolsize / getpagesize() * BITS_PER_PAGE,
-				CHAR_BIT);
-	if (metalen < (sizeof(unsigned long)
-		       + align_up(pagestatebytes, ALIGNOF(unsigned long))
-		       + sizeof(unsigned long)))
-		return false;
+	/* First check metadata pages. */
+	/* Metadata pages will be marked TAKEN. */
+	for (mh = first_mheader(pool,poolsize); mh; mh = next_mheader(pool,mh)){
+		unsigned long start, end;
 
-	for (i = 1; i < poolsize / getpagesize(); i++) {
-		enum page_state state = get_page_state(pool, i);
+		start = pool_offset(pool, mh);
+		if (start + sizeof(*mh) > poolsize)
+			return false;
 
-		/* Metadata pages will be marked TAKEN. */
-		if (i < div_up(metalen, getpagesize())) {
-			if (get_page_state(pool, 0) != TAKEN)
-				return false;
-			continue;
-		}
+		end = pool_offset(pool, (char *)(mh+1) + mh->metalen);
+		if (end > poolsize)
+			return false;
+
+		/* Non-first pages should start on a page boundary. */
+		if (mh != first_mheader(pool, poolsize)
+		    && start % getpagesize() != 0)
+			return false;
+
+		/* It should end on a page boundary. */
+		if (end % getpagesize() != 0)
+			return false;
+	}
+
+	for (i = 0; i < poolsize / getpagesize(); i++) {
+		enum page_state state = get_page_state(pool, i);
+		bool is_metadata = is_metadata_page(pool, poolsize,i);
 
 		switch (state) {
 		case FREE:
+			/* metadata pages are never free. */
+			if (is_metadata)
+				return false;
 		case TAKEN_START:
 			break;
 		case TAKEN:
+			/* This should continue a previous block. */
 			if (last_state == FREE)
 				return false;
+			if (is_metadata != was_metadata)
+				return false;
 			break;
-		default:
-			return false;
+		case SUBPAGE:
+			/* Check metadata pointer etc. */
+			if (!check_subpage(pool, poolsize, i))
+				return false;
 		}
 		last_state = state;
+		was_metadata = is_metadata;
 	}
 	return true;
 }

alloc/test/run.c

@@ -24,13 +24,32 @@ static bool unique(void *p[], unsigned int num)
 	return true;
 }	
 
+static bool free_every_second_one(void *mem, unsigned int num, void *p[])
+{
+	unsigned int i;
+
+	/* Free every second one. */
+	for (i = 0; i < num; i += 2) {
+		alloc_free(mem, POOL_SIZE, p[i]);
+		if (!alloc_check(mem, POOL_SIZE))
+			return false;
+	}
+	for (i = 1; i < num; i += 2) {
+		alloc_free(mem, POOL_SIZE, p[i]);
+		if (!alloc_check(mem, POOL_SIZE))
+			return false;
+	}
+	return true;
+}
+
+
 int main(int argc, char *argv[])
 {
 	void *mem;
 	unsigned int i, num, max_size;
 	void *p[POOL_SIZE];
 
-	plan_tests(141);
+	plan_tests(133);
 
 	/* FIXME: Needs to be page aligned for now. */
 	posix_memalign(&mem, getpagesize(), POOL_SIZE);
@@ -85,15 +104,7 @@ int main(int argc, char *argv[])
 	/* Uniqueness check */
 	ok1(unique(p, num));
 
-	/* Free every second one. */
-	for (i = 0; i < num; i += 2) {
-		alloc_free(mem, POOL_SIZE, p[i]);
-		ok1(alloc_check(mem, POOL_SIZE));
-	}
-	for (i = 1; i < num; i += 2) {
-		alloc_free(mem, POOL_SIZE, p[i]);
-		ok1(alloc_check(mem, POOL_SIZE));
-	}
+	ok1(free_every_second_one(mem, num, p));
 	ok1(alloc_check(mem, POOL_SIZE));
 
 	/* Should be able to reallocate max size. */
@@ -111,14 +122,14 @@ int main(int argc, char *argv[])
 	ok1(alloc_check(mem, POOL_SIZE));
 
 	/* Alignment constraints should be met, as long as powers of two */
-	for (i = 0; i < POOL_ORD-2 /* FIXME: Should be -1 */; i++) {
+	for (i = 0; i < POOL_ORD-1; i++) {
 		p[i] = alloc_get(mem, POOL_SIZE, i, 1 << i);
 		ok1(p[i]);
 		ok1(((unsigned long)p[i] % (1 << i)) == 0);
 		ok1(alloc_check(mem, POOL_SIZE));
 	}
 
-	for (i = 0; i < POOL_ORD-2 /* FIXME: Should be -1 */; i++) {
+	for (i = 0; i < POOL_ORD-1; i++) {
 		alloc_free(mem, POOL_SIZE, p[i]);
 		ok1(alloc_check(mem, POOL_SIZE));
 	}
@@ -132,5 +143,11 @@ int main(int argc, char *argv[])
 		ok1(alloc_check(mem, POOL_SIZE));
 	}
 
+	/* Alignment check for a 0-byte allocation.  Corner case. */
+	p[0] = alloc_get(mem, POOL_SIZE, 0, 1 << (POOL_ORD - 1));
+	ok1(alloc_check(mem, POOL_SIZE));
+	alloc_free(mem, POOL_SIZE, p[0]);
+	ok1(alloc_check(mem, POOL_SIZE));
+
 	return exit_status();
 }