slob: implement RCU freeing
The SLOB allocator should implement SLAB_DESTROY_BY_RCU correctly, because
even on UP, RCU freeing semantics are not equivalent to simply freeing
immediately. This also allows SLOB to be used on SMP.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/slob.c b/mm/slob.c
index c6933bc..57bb72e 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -35,6 +35,7 @@
#include <linux/init.h>
#include <linux/module.h>
#include <linux/timer.h>
+#include <linux/rcupdate.h>
struct slob_block {
int units;
@@ -53,6 +54,16 @@
};
typedef struct bigblock bigblock_t;
+/*
+ * struct slob_rcu is inserted at the tail of allocated slob blocks, which
+ * were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
+ * the block using call_rcu.
+ */
+struct slob_rcu {
+ struct rcu_head head;
+ int size;
+};
+
static slob_t arena = { .next = &arena, .units = 1 };
static slob_t *slobfree = &arena;
static bigblock_t *bigblocks;
@@ -266,6 +277,7 @@
struct kmem_cache {
unsigned int size, align;
+ unsigned long flags;
const char *name;
void (*ctor)(void *, struct kmem_cache *, unsigned long);
void (*dtor)(void *, struct kmem_cache *, unsigned long);
@@ -283,6 +295,12 @@
if (c) {
c->name = name;
c->size = size;
+ if (flags & SLAB_DESTROY_BY_RCU) {
+ BUG_ON(dtor);
+ /* leave room for rcu footer at the end of object */
+ c->size += sizeof(struct slob_rcu);
+ }
+ c->flags = flags;
c->ctor = ctor;
c->dtor = dtor;
/* ignore alignment unless it's forced */
@@ -328,15 +346,35 @@
}
EXPORT_SYMBOL(kmem_cache_zalloc);
+static void __kmem_cache_free(void *b, int size)
+{
+ if (size < PAGE_SIZE)
+ slob_free(b, size);
+ else
+ free_pages((unsigned long)b, get_order(size));
+}
+
+static void kmem_rcu_free(struct rcu_head *head)
+{
+ struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
+ void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));
+
+ __kmem_cache_free(b, slob_rcu->size);
+}
+
void kmem_cache_free(struct kmem_cache *c, void *b)
{
- if (c->dtor)
- c->dtor(b, c, 0);
-
- if (c->size < PAGE_SIZE)
- slob_free(b, c->size);
- else
- free_pages((unsigned long)b, get_order(c->size));
+ if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
+ struct slob_rcu *slob_rcu;
+ slob_rcu = b + (c->size - sizeof(struct slob_rcu));
+ INIT_RCU_HEAD(&slob_rcu->head);
+ slob_rcu->size = c->size;
+ call_rcu(&slob_rcu->head, kmem_rcu_free);
+ } else {
+ if (c->dtor)
+ c->dtor(b, c, 0);
+ __kmem_cache_free(b, c->size);
+ }
}
EXPORT_SYMBOL(kmem_cache_free);