slub: Store max number of objects in the page struct.

Split the inuse field up to be able to store the number of objects in this
page in the page struct as well. Necessary if we want to have pages of
various orders for a slab. Also avoids touching struct kmem_cache cachelines in
__slab_alloc().

Update diagnostic code to check the number of objects and make sure that
the number of objects always stays within the bounds of a 16 bit unsigned
integer.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

2 files changed, 38 insertions, 21 deletions

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index af190ce..e0bd223 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -42,7 +42,10 @@ struct page {
 					 * to show when page is mapped
 					 * & limit reverse map searches.
 					 */
-		unsigned int inuse;	/* SLUB: Nr of objects */
+		struct {		/* SLUB */
+			u16 inuse;
+			u16 objects;
+		};
 	};
 	union {
 	    struct {
diff --git a/mm/slub.c b/mm/slub.c
index 64c2b2b..6641025 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -301,7 +301,7 @@ static inline int check_valid_pointer(struct kmem_cache *s,
 		return 1;
 
 	base = page_address(page);
-	if (object < base || object >= base + s->objects * s->size ||
+	if (object < base || object >= base + page->objects * s->size ||
 		(object - base) % s->size) {
 		return 0;
 	}
@@ -451,8 +451,8 @@ static void print_tracking(struct kmem_cache *s, void *object)
 
 static void print_page_info(struct page *page)
 {
-	printk(KERN_ERR "INFO: Slab 0x%p used=%u fp=0x%p flags=0x%04lx\n",
-		page, page->inuse, page->freelist, page->flags);
+	printk(KERN_ERR "INFO: Slab 0x%p objects=%u used=%u fp=0x%p flags=0x%04lx\n",
+		page, page->objects, page->inuse, page->freelist, page->flags);
 
 }
 
@@ -652,6 +652,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct page *page, u8 *p)
 				p + off, POISON_INUSE, s->size - off);
 }
 
+/* Check the pad bytes at the end of a slab page */
 static int slab_pad_check(struct kmem_cache *s, struct page *page)
 {
 	u8 *start;
@@ -664,20 +665,20 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page)
 		return 1;
 
 	start = page_address(page);
-	end = start + (PAGE_SIZE << s->order);
-	length = s->objects * s->size;
-	remainder = end - (start + length);
+	length = (PAGE_SIZE << s->order);
+	end = start + length;
+	remainder = length % s->size;
 	if (!remainder)
 		return 1;
 
-	fault = check_bytes(start + length, POISON_INUSE, remainder);
+	fault = check_bytes(end - remainder, POISON_INUSE, remainder);
 	if (!fault)
 		return 1;
 	while (end > fault && end[-1] == POISON_INUSE)
 		end--;
 
 	slab_err(s, page, "Padding overwritten. 0x%p-0x%p", fault, end - 1);
-	print_section("Padding", start, length);
+	print_section("Padding", end - remainder, remainder);
 
 	restore_bytes(s, "slab padding", POISON_INUSE, start, end);
 	return 0;
@@ -739,15 +740,24 @@ static int check_object(struct kmem_cache *s, struct page *page,
 
 static int check_slab(struct kmem_cache *s, struct page *page)
 {
+	int maxobj;
+
 	VM_BUG_ON(!irqs_disabled());
 
 	if (!PageSlab(page)) {
 		slab_err(s, page, "Not a valid slab page");
 		return 0;
 	}
-	if (page->inuse > s->objects) {
+
+	maxobj = (PAGE_SIZE << compound_order(page)) / s->size;
+	if (page->objects > maxobj) {
+		slab_err(s, page, "objects %u > max %u",
+			s->name, page->objects, maxobj);
+		return 0;
+	}
+	if (page->inuse > page->objects) {
 		slab_err(s, page, "inuse %u > max %u",
-			s->name, page->inuse, s->objects);
+			s->name, page->inuse, page->objects);
 		return 0;
 	}
 	/* Slab_pad_check fixes things up after itself */
@@ -765,7 +775,7 @@ static int on_freelist(struct kmem_cache *s, struct page *page, void *search)
 	void *fp = page->freelist;
 	void *object = NULL;
 
-	while (fp && nr <= s->objects) {
+	while (fp && nr <= page->objects) {
 		if (fp == search)
 			return 1;
 		if (!check_valid_pointer(s, page, fp)) {
@@ -777,7 +787,7 @@ static int on_freelist(struct kmem_cache *s, struct page *page, void *search)
 			} else {
 				slab_err(s, page, "Freepointer corrupt");
 				page->freelist = NULL;
-				page->inuse = s->objects;
+				page->inuse = page->objects;
 				slab_fix(s, "Freelist cleared");
 				return 0;
 			}
@@ -788,10 +798,10 @@ static int on_freelist(struct kmem_cache *s, struct page *page, void *search)
 		nr++;
 	}
 
-	if (page->inuse != s->objects - nr) {
+	if (page->inuse != page->objects - nr) {
 		slab_err(s, page, "Wrong object count. Counter is %d but "
-			"counted were %d", page->inuse, s->objects - nr);
-		page->inuse = s->objects - nr;
+			"counted were %d", page->inuse, page->objects - nr);
+		page->inuse = page->objects - nr;
 		slab_fix(s, "Object count adjusted.");
 	}
 	return search == NULL;
@@ -910,7 +920,7 @@ bad:
 		 * as used avoids touching the remaining objects.
 		 */
 		slab_fix(s, "Marking all objects used");
-		page->inuse = s->objects;
+		page->inuse = page->objects;
 		page->freelist = NULL;
 	}
 	return 0;
@@ -1081,6 +1091,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
 	if (!page)
 		return NULL;
 
+	page->objects = s->objects;
 	mod_zone_page_state(page_zone(page),
 		(s->flags & SLAB_RECLAIM_ACCOUNT) ?
 		NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,
@@ -1519,7 +1530,7 @@ load_freelist:
 		goto debug;
 
 	c->freelist = object[c->offset];
-	c->page->inuse = s->objects;
+	c->page->inuse = c->page->objects;
 	c->page->freelist = NULL;
 	c->node = page_to_nid(c->page);
 unlock_out:
@@ -1818,6 +1829,9 @@ static inline int slab_order(int size, int min_objects,
 	int rem;
 	int min_order = slub_min_order;
 
+	if ((PAGE_SIZE << min_order) / size > 65535)
+		return get_order(size * 65535) - 1;
+
 	for (order = max(min_order,
 				fls(min_objects * size - 1) - PAGE_SHIFT);
 			order <= max_order; order++) {
@@ -3251,7 +3265,7 @@ static int validate_slab(struct kmem_cache *s, struct page *page,
 		return 0;
 
 	/* Now we know that a valid freelist exists */
-	bitmap_zero(map, s->objects);
+	bitmap_zero(map, page->objects);
 
 	for_each_free_object(p, s, page->freelist) {
 		set_bit(slab_index(p, s, addr), map);
@@ -3528,10 +3542,10 @@ static void process_slab(struct loc_track *t, struct kmem_cache *s,
 		struct page *page, enum track_item alloc)
 {
 	void *addr = page_address(page);
-	DECLARE_BITMAP(map, s->objects);
+	DECLARE_BITMAP(map, page->objects);
 	void *p;
 
-	bitmap_zero(map, s->objects);
+	bitmap_zero(map, page->objects);
 	for_each_free_object(p, s, page->freelist)
 		set_bit(slab_index(p, s, addr), map);