diff options
| -rw-r--r-- | include/linux/mm_types.h | 3 | ||||
| -rw-r--r-- | include/linux/slab.h | 9 | ||||
| -rw-r--r-- | mm/slab.c | 68 |
3 files changed, 41 insertions, 39 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index faf4b7c1ad12..959cb369b197 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -130,6 +130,9 @@ struct page { struct list_head list; /* slobs list of pages */ struct slab *slab_page; /* slab fields */ + struct rcu_head rcu_head; /* Used by SLAB + * when destroying via RCU + */ }; /* Remainder is not double word aligned */ diff --git a/include/linux/slab.h b/include/linux/slab.h index 6c5cc0ea8713..caaad51fee1f 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -51,7 +51,14 @@ * } * rcu_read_unlock(); * - * See also the comment on struct slab_rcu in mm/slab.c. + * This is useful if we need to approach a kernel structure obliquely, + * from its address obtained without the usual locking. We can lock + * the structure to stabilize it and check it's still at the given address, + * only if we can be sure that the memory has not been meanwhile reused + * for some other kind of object (which our subsystem's lock might corrupt). + * + * rcu_read_lock before reading the address, then rcu_read_unlock after + * taking the spinlock within the structure expected at that address. */ #define SLAB_DESTROY_BY_RCU 0x00080000UL /* Defer freeing slabs to RCU */ #define SLAB_MEM_SPREAD 0x00100000UL /* Spread some memory over cpuset */ diff --git a/mm/slab.c b/mm/slab.c index 7e1aabe2b5d8..84c4ed62c10d 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -189,25 +189,6 @@ typedef unsigned int kmem_bufctl_t; #define SLAB_LIMIT (((kmem_bufctl_t)(~0U))-3) /* - * struct slab_rcu - * - * slab_destroy on a SLAB_DESTROY_BY_RCU cache uses this structure to - * arrange for kmem_freepages to be called via RCU. This is useful if - * we need to approach a kernel structure obliquely, from its address - * obtained without the usual locking. We can lock the structure to - * stabilize it and check it's still at the given address, only if we - * can be sure that the memory has not been meanwhile reused for some - * other kind of object (which our subsystem's lock might corrupt). - * - * rcu_read_lock before reading the address, then rcu_read_unlock after - * taking the spinlock within the structure expected at that address. - */ -struct slab_rcu { - struct rcu_head head; - struct page *page; -}; - -/* * struct slab * * Manages the objs in a slab. Placed either at the beginning of mem allocated @@ -215,14 +196,11 @@ struct slab_rcu { * Slabs are chained into three list: fully used, partial, fully free slabs. */ struct slab { - union { - struct { - struct list_head list; - void *s_mem; /* including colour offset */ - unsigned int inuse; /* num of objs active in slab */ - kmem_bufctl_t free; - }; - struct slab_rcu __slab_cover_slab_rcu; + struct { + struct list_head list; + void *s_mem; /* including colour offset */ + unsigned int inuse; /* num of objs active in slab */ + kmem_bufctl_t free; }; }; @@ -1509,6 +1487,8 @@ void __init kmem_cache_init(void) { int i; + BUILD_BUG_ON(sizeof(((struct page *)NULL)->lru) < + sizeof(struct rcu_head)); kmem_cache = &kmem_cache_boot; setup_node_pointer(kmem_cache); @@ -1822,12 +1802,13 @@ static void kmem_freepages(struct kmem_cache *cachep, struct page *page) static void kmem_rcu_free(struct rcu_head *head) { - struct slab_rcu *slab_rcu = (struct slab_rcu *)head; - struct kmem_cache *cachep = slab_rcu->page->slab_cache; + struct kmem_cache *cachep; + struct page *page; - kmem_freepages(cachep, slab_rcu->page); - if (OFF_SLAB(cachep)) - kmem_cache_free(cachep->slabp_cache, slab_rcu); + page = container_of(head, struct page, rcu_head); + cachep = page->slab_cache; + + kmem_freepages(cachep, page); } #if DEBUG @@ -2048,16 +2029,27 @@ static void slab_destroy(struct kmem_cache *cachep, struct slab *slabp) slab_destroy_debugcheck(cachep, slabp); if (unlikely(cachep->flags & SLAB_DESTROY_BY_RCU)) { - struct slab_rcu *slab_rcu; + struct rcu_head *head; + + /* + * RCU free overloads the RCU head over the LRU. + * slab_page has been overloeaded over the LRU, + * however it is not used from now on so that + * we can use it safely. + */ + head = (void *)&page->rcu_head; + call_rcu(head, kmem_rcu_free); - slab_rcu = (struct slab_rcu *)slabp; - slab_rcu->page = page; - call_rcu(&slab_rcu->head, kmem_rcu_free); } else { kmem_freepages(cachep, page); - if (OFF_SLAB(cachep)) - kmem_cache_free(cachep->slabp_cache, slabp); } + + /* + * From now on, we don't use slab management + * although actual page can be freed in rcu context + */ + if (OFF_SLAB(cachep)) + kmem_cache_free(cachep->slabp_cache, slabp); } /** |