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Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/penberg/slab-2.6

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* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/penberg/slab-2.6:
  slab: document SLAB_DESTROY_BY_RCU
  Kconfig: SLUB is the default slab allocator
This commit is contained in:
Linus Torvalds 2008-11-13 11:30:46 -08:00
commit 2d1595ad87
2 changed files with 31 additions and 3 deletions
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28
include/linux/slab.h
View File

@ -23,6 +23,34 @@
#define SLAB_CACHE_DMA 0x00004000UL /* Use GFP_DMA memory */
#define SLAB_STORE_USER 0x00010000UL /* DEBUG: Store the last owner for bug hunting */
#define SLAB_PANIC 0x00040000UL /* Panic if kmem_cache_create() fails */
/*
* SLAB_DESTROY_BY_RCU - **WARNING** READ THIS!
*
* This delays freeing the SLAB page by a grace period, it does _NOT_
* delay object freeing. This means that if you do kmem_cache_free()
* that memory location is free to be reused at any time. Thus it may
* be possible to see another object there in the same RCU grace period.
*
* This feature only ensures the memory location backing the object
* stays valid, the trick to using this is relying on an independent
* object validation pass. Something like:
*
* rcu_read_lock()
* again:
* obj = lockless_lookup(key);
* if (obj) {
* if (!try_get_ref(obj)) // might fail for free objects
* goto again;
*
* if (obj->key != key) { // not the object we expected
* put_ref(obj);
* goto again;
* }
* }
* rcu_read_unlock();
*
* See also the comment on struct slab_rcu in mm/slab.c.
*/
#define SLAB_DESTROY_BY_RCU 0x00080000UL /* Defer freeing slabs to RCU */
#define SLAB_MEM_SPREAD 0x00100000UL /* Spread some memory over cpuset */
#define SLAB_TRACE 0x00200000UL /* Trace allocations and frees */

6
init/Kconfig
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@ -771,8 +771,7 @@ config SLAB
help
The regular slab allocator that is established and known to work
well in all environments. It organizes cache hot objects in
per cpu and per node queues. SLAB is the default choice for
a slab allocator.
per cpu and per node queues.
config SLUB
bool "SLUB (Unqueued Allocator)"
@ -781,7 +780,8 @@ config SLUB
instead of managing queues of cached objects (SLAB approach).
Per cpu caching is realized using slabs of objects instead
of queues of objects. SLUB can use memory efficiently
and has enhanced diagnostics.
and has enhanced diagnostics. SLUB is the default choice for
a slab allocator.
config SLOB
depends on EMBEDDED