slub: automatically reserve bytes at the end of slab
There is no "struct" for slub's slab, it shares with struct page.
But struct page is very small, it is insufficient when we need
to add some metadata for slab.
So we add a field "reserved" to struct kmem_cache, when a slab
is allocated, kmem_cache->reserved bytes are automatically reserved
at the end of the slab for slab's metadata.
Changed from v1:
Export the reserved field via sysfs
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
diff --git a/mm/slub.c b/mm/slub.c
index e15aa7f..d3d1767 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -281,11 +281,16 @@
return (p - addr) / s->size;
}
+static inline int order_objects(int order, unsigned long size, int reserved)
+{
+ return ((PAGE_SIZE << order) - reserved) / size;
+}
+
static inline struct kmem_cache_order_objects oo_make(int order,
- unsigned long size)
+ unsigned long size, int reserved)
{
struct kmem_cache_order_objects x = {
- (order << OO_SHIFT) + (PAGE_SIZE << order) / size
+ (order << OO_SHIFT) + order_objects(order, size, reserved)
};
return x;
@@ -617,7 +622,7 @@
return 1;
start = page_address(page);
- length = (PAGE_SIZE << compound_order(page));
+ length = (PAGE_SIZE << compound_order(page)) - s->reserved;
end = start + length;
remainder = length % s->size;
if (!remainder)
@@ -698,7 +703,7 @@
return 0;
}
- maxobj = (PAGE_SIZE << compound_order(page)) / s->size;
+ maxobj = order_objects(compound_order(page), s->size, s->reserved);
if (page->objects > maxobj) {
slab_err(s, page, "objects %u > max %u",
s->name, page->objects, maxobj);
@@ -748,7 +753,7 @@
nr++;
}
- max_objects = (PAGE_SIZE << compound_order(page)) / s->size;
+ max_objects = order_objects(compound_order(page), s->size, s->reserved);
if (max_objects > MAX_OBJS_PER_PAGE)
max_objects = MAX_OBJS_PER_PAGE;
@@ -1988,13 +1993,13 @@
* the smallest order which will fit the object.
*/
static inline int slab_order(int size, int min_objects,
- int max_order, int fract_leftover)
+ int max_order, int fract_leftover, int reserved)
{
int order;
int rem;
int min_order = slub_min_order;
- if ((PAGE_SIZE << min_order) / size > MAX_OBJS_PER_PAGE)
+ if (order_objects(min_order, size, reserved) > MAX_OBJS_PER_PAGE)
return get_order(size * MAX_OBJS_PER_PAGE) - 1;
for (order = max(min_order,
@@ -2003,10 +2008,10 @@
unsigned long slab_size = PAGE_SIZE << order;
- if (slab_size < min_objects * size)
+ if (slab_size < min_objects * size + reserved)
continue;
- rem = slab_size % size;
+ rem = (slab_size - reserved) % size;
if (rem <= slab_size / fract_leftover)
break;
@@ -2016,7 +2021,7 @@
return order;
}
-static inline int calculate_order(int size)
+static inline int calculate_order(int size, int reserved)
{
int order;
int min_objects;
@@ -2034,14 +2039,14 @@
min_objects = slub_min_objects;
if (!min_objects)
min_objects = 4 * (fls(nr_cpu_ids) + 1);
- max_objects = (PAGE_SIZE << slub_max_order)/size;
+ max_objects = order_objects(slub_max_order, size, reserved);
min_objects = min(min_objects, max_objects);
while (min_objects > 1) {
fraction = 16;
while (fraction >= 4) {
order = slab_order(size, min_objects,
- slub_max_order, fraction);
+ slub_max_order, fraction, reserved);
if (order <= slub_max_order)
return order;
fraction /= 2;
@@ -2053,14 +2058,14 @@
* We were unable to place multiple objects in a slab. Now
* lets see if we can place a single object there.
*/
- order = slab_order(size, 1, slub_max_order, 1);
+ order = slab_order(size, 1, slub_max_order, 1, reserved);
if (order <= slub_max_order)
return order;
/*
* Doh this slab cannot be placed using slub_max_order.
*/
- order = slab_order(size, 1, MAX_ORDER, 1);
+ order = slab_order(size, 1, MAX_ORDER, 1, reserved);
if (order < MAX_ORDER)
return order;
return -ENOSYS;
@@ -2311,7 +2316,7 @@
if (forced_order >= 0)
order = forced_order;
else
- order = calculate_order(size);
+ order = calculate_order(size, s->reserved);
if (order < 0)
return 0;
@@ -2329,8 +2334,8 @@
/*
* Determine the number of objects per slab
*/
- s->oo = oo_make(order, size);
- s->min = oo_make(get_order(size), size);
+ s->oo = oo_make(order, size, s->reserved);
+ s->min = oo_make(get_order(size), size, s->reserved);
if (oo_objects(s->oo) > oo_objects(s->max))
s->max = s->oo;
@@ -2349,6 +2354,7 @@
s->objsize = size;
s->align = align;
s->flags = kmem_cache_flags(size, flags, name, ctor);
+ s->reserved = 0;
if (!calculate_sizes(s, -1))
goto error;
@@ -4017,6 +4023,12 @@
}
SLAB_ATTR_RO(destroy_by_rcu);
+static ssize_t reserved_show(struct kmem_cache *s, char *buf)
+{
+ return sprintf(buf, "%d\n", s->reserved);
+}
+SLAB_ATTR_RO(reserved);
+
#ifdef CONFIG_SLUB_DEBUG
static ssize_t slabs_show(struct kmem_cache *s, char *buf)
{
@@ -4303,6 +4315,7 @@
&reclaim_account_attr.attr,
&destroy_by_rcu_attr.attr,
&shrink_attr.attr,
+ &reserved_attr.attr,
#ifdef CONFIG_SLUB_DEBUG
&total_objects_attr.attr,
&slabs_attr.attr,