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-rw-r--r--include/linux/slab.h28
1 files changed, 28 insertions, 0 deletions
diff --git a/include/linux/slab.h b/include/linux/slab.h
index ba965c84ae06..000da12b5cf0 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -23,6 +23,34 @@
23#define SLAB_CACHE_DMA 0x00004000UL /* Use GFP_DMA memory */ 23#define SLAB_CACHE_DMA 0x00004000UL /* Use GFP_DMA memory */
24#define SLAB_STORE_USER 0x00010000UL /* DEBUG: Store the last owner for bug hunting */ 24#define SLAB_STORE_USER 0x00010000UL /* DEBUG: Store the last owner for bug hunting */
25#define SLAB_PANIC 0x00040000UL /* Panic if kmem_cache_create() fails */ 25#define SLAB_PANIC 0x00040000UL /* Panic if kmem_cache_create() fails */
26/*
27 * SLAB_DESTROY_BY_RCU - **WARNING** READ THIS!
28 *
29 * This delays freeing the SLAB page by a grace period, it does _NOT_
30 * delay object freeing. This means that if you do kmem_cache_free()
31 * that memory location is free to be reused at any time. Thus it may
32 * be possible to see another object there in the same RCU grace period.
33 *
34 * This feature only ensures the memory location backing the object
35 * stays valid, the trick to using this is relying on an independent
36 * object validation pass. Something like:
37 *
38 * rcu_read_lock()
39 * again:
40 * obj = lockless_lookup(key);
41 * if (obj) {
42 * if (!try_get_ref(obj)) // might fail for free objects
43 * goto again;
44 *
45 * if (obj->key != key) { // not the object we expected
46 * put_ref(obj);
47 * goto again;
48 * }
49 * }
50 * rcu_read_unlock();
51 *
52 * See also the comment on struct slab_rcu in mm/slab.c.
53 */
26#define SLAB_DESTROY_BY_RCU 0x00080000UL /* Defer freeing slabs to RCU */ 54#define SLAB_DESTROY_BY_RCU 0x00080000UL /* Defer freeing slabs to RCU */
27#define SLAB_MEM_SPREAD 0x00100000UL /* Spread some memory over cpuset */ 55#define SLAB_MEM_SPREAD 0x00100000UL /* Spread some memory over cpuset */
28#define SLAB_TRACE 0x00200000UL /* Trace allocations and frees */ 56#define SLAB_TRACE 0x00200000UL /* Trace allocations and frees */