[PATCH] cpuset memory spread slab cache implementation

Provide the slab cache infrastructure to support cpuset memory spreading.

See the previous patches, cpuset_mem_spread, for an explanation of cpuset
memory spreading.

This patch provides a slab cache SLAB_MEM_SPREAD flag.  If set in the
kmem_cache_create() call defining a slab cache, then any task marked with the
process state flag PF_MEMSPREAD will spread memory page allocations for that
cache over all the allowed nodes, instead of preferring the local (faulting)
node.

On systems not configured with CONFIG_NUMA, this results in no change to the
page allocation code path for slab caches.

On systems with cpusets configured in the kernel, but the "memory_spread"
cpuset option not enabled for the current tasks cpuset, this adds a call to a
cpuset routine and failed bit test of the processor state flag PF_SPREAD_SLAB.

For tasks so marked, a second inline test is done for the slab cache flag
SLAB_MEM_SPREAD, and if that is set and if the allocation is not
in_interrupt(), this adds a call to to a cpuset routine that computes which of
the tasks mems_allowed nodes should be preferred for this allocation.

==> This patch adds another hook into the performance critical
    code path to allocating objects from the slab cache, in the
    ____cache_alloc() chunk, below.  The next patch optimizes this
    hook, reducing the impact of the combined mempolicy plus memory
    spreading hooks on this critical code path to a single check
    against the tasks task_struct flags word.

This patch provides the generic slab flags and logic needed to apply memory
spreading to a particular slab.

A subsequent patch will mark a few specific slab caches for this placement
policy.
Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/slab.h

@@ -46,6 +46,7 @@ typedef struct kmem_cache kmem_cache_t;
 						   what is reclaimable later*/
 #define SLAB_PANIC		0x00040000UL	/* panic if kmem_cache_create() fails */
 #define SLAB_DESTROY_BY_RCU	0x00080000UL	/* defer freeing pages to RCU */
+#define SLAB_MEM_SPREAD		0x00100000UL	/* Spread some memory over cpuset */
 
 /* flags passed to a constructor func */
 #define	SLAB_CTOR_CONSTRUCTOR	0x001UL		/* if not set, then deconstructor */

mm/slab.c

@@ -94,6 +94,7 @@
 #include	<linux/interrupt.h>
 #include	<linux/init.h>
 #include	<linux/compiler.h>
+#include	<linux/cpuset.h>
 #include	<linux/seq_file.h>
 #include	<linux/notifier.h>
 #include	<linux/kallsyms.h>
@@ -173,12 +174,12 @@
 			 SLAB_CACHE_DMA | \
 			 SLAB_MUST_HWCACHE_ALIGN | SLAB_STORE_USER | \
 			 SLAB_RECLAIM_ACCOUNT | SLAB_PANIC | \
-			 SLAB_DESTROY_BY_RCU)
+			 SLAB_DESTROY_BY_RCU | SLAB_MEM_SPREAD)
 #else
 # define CREATE_MASK	(SLAB_HWCACHE_ALIGN | \
 			 SLAB_CACHE_DMA | SLAB_MUST_HWCACHE_ALIGN | \
 			 SLAB_RECLAIM_ACCOUNT | SLAB_PANIC | \
-			 SLAB_DESTROY_BY_RCU)
+			 SLAB_DESTROY_BY_RCU | SLAB_MEM_SPREAD)
 #endif
 
 /*
@@ -2810,6 +2811,14 @@ static inline void *____cache_alloc(struct kmem_cache *cachep, gfp_t flags)
 	if (unlikely(current->mempolicy && !in_interrupt())) {
 		int nid = slab_node(current->mempolicy);
 
+		if (nid != numa_node_id())
+			return __cache_alloc_node(cachep, flags, nid);
+	}
+	if (unlikely(cpuset_do_slab_mem_spread() &&
+					(cachep->flags & SLAB_MEM_SPREAD) &&
+					!in_interrupt())) {
+		int nid = cpuset_mem_spread_node();
+
 		if (nid != numa_node_id())
 			return __cache_alloc_node(cachep, flags, nid);
 	}