From 02f5621042e3f7e2fb6c741cbe5ee7c1f3caf354 Mon Sep 17 00:00:00 2001 From: Simon Arlott Date: Wed, 5 Nov 2008 22:18:19 +0000 Subject: [PATCH 1/2] Kconfig: SLUB is the default slab allocator In 2007, a0acd820807680d2ccc4ef3448387fcdbf152c73 changed the default slab allocator to SLUB, but the SLAB help text still says SLAB is the default. This change fixes that. Signed-off-by: Simon Arlott Signed-off-by: Pekka Enberg --- init/Kconfig | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 86b00c53fade..226da2733c1e 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -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 From d7de4c1dc3a2faca0bf05d9e342f885cb2696766 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 13 Nov 2008 20:40:12 +0200 Subject: [PATCH 2/2] slab: document SLAB_DESTROY_BY_RCU Explain this SLAB_DESTROY_BY_RCU thing... [hugh@veritas.com: add a pointer to comment in mm/slab.c] Signed-off-by: Peter Zijlstra Acked-by: Jens Axboe Acked-by: Paul E. McKenney Acked-by: Christoph Lameter Signed-off-by: Hugh Dickins Signed-off-by: Pekka Enberg --- include/linux/slab.h | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) 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 @@ #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 */