SLUB core

This is a new slab allocator which was motivated by the complexity of the
existing code in mm/slab.c. It attempts to address a variety of concerns
with the existing implementation.

A. Management of object queues

   A particular concern was the complex management of the numerous object
   queues in SLAB. SLUB has no such queues. Instead we dedicate a slab for
   each allocating CPU and use objects from a slab directly instead of
   queueing them up.

B. Storage overhead of object queues

   SLAB Object queues exist per node, per CPU. The alien cache queue even
   has a queue array that contain a queue for each processor on each
   node. For very large systems the number of queues and the number of
   objects that may be caught in those queues grows exponentially. On our
   systems with 1k nodes / processors we have several gigabytes just tied up
   for storing references to objects for those queues  This does not include
   the objects that could be on those queues. One fears that the whole
   memory of the machine could one day be consumed by those queues.

C. SLAB meta data overhead

   SLAB has overhead at the beginning of each slab. This means that data
   cannot be naturally aligned at the beginning of a slab block. SLUB keeps
   all meta data in the corresponding page_struct. Objects can be naturally
   aligned in the slab. F.e. a 128 byte object will be aligned at 128 byte
   boundaries and can fit tightly into a 4k page with no bytes left over.
   SLAB cannot do this.

D. SLAB has a complex cache reaper

   SLUB does not need a cache reaper for UP systems. On SMP systems
   the per CPU slab may be pushed back into partial list but that
   operation is simple and does not require an iteration over a list
   of objects. SLAB expires per CPU, shared and alien object queues
   during cache reaping which may cause strange hold offs.

E. SLAB has complex NUMA policy layer support

   SLUB pushes NUMA policy handling into the page allocator. This means that
   allocation is coarser (SLUB does interleave on a page level) but that
   situation was also present before 2.6.13. SLABs application of
   policies to individual slab objects allocated in SLAB is
   certainly a performance concern due to the frequent references to
   memory policies which may lead a sequence of objects to come from
   one node after another. SLUB will get a slab full of objects
   from one node and then will switch to the next.

F. Reduction of the size of partial slab lists

   SLAB has per node partial lists. This means that over time a large
   number of partial slabs may accumulate on those lists. These can
   only be reused if allocator occur on specific nodes. SLUB has a global
   pool of partial slabs and will consume slabs from that pool to
   decrease fragmentation.

G. Tunables

   SLAB has sophisticated tuning abilities for each slab cache. One can
   manipulate the queue sizes in detail. However, filling the queues still
   requires the uses of the spin lock to check out slabs. SLUB has a global
   parameter (min_slab_order) for tuning. Increasing the minimum slab
   order can decrease the locking overhead. The bigger the slab order the
   less motions of pages between per CPU and partial lists occur and the
   better SLUB will be scaling.

G. Slab merging

   We often have slab caches with similar parameters. SLUB detects those
   on boot up and merges them into the corresponding general caches. This
   leads to more effective memory use. About 50% of all caches can
   be eliminated through slab merging. This will also decrease
   slab fragmentation because partial allocated slabs can be filled
   up again. Slab merging can be switched off by specifying
   slub_nomerge on boot up.

   Note that merging can expose heretofore unknown bugs in the kernel
   because corrupted objects may now be placed differently and corrupt
   differing neighboring objects. Enable sanity checks to find those.

H. Diagnostics

   The current slab diagnostics are difficult to use and require a
   recompilation of the kernel. SLUB contains debugging code that
   is always available (but is kept out of the hot code paths).
   SLUB diagnostics can be enabled via the "slab_debug" option.
   Parameters can be specified to select a single or a group of
   slab caches for diagnostics. This means that the system is running
   with the usual performance and it is much more likely that
   race conditions can be reproduced.

I. Resiliency

   If basic sanity checks are on then SLUB is capable of detecting
   common error conditions and recover as best as possible to allow the
   system to continue.

J. Tracing

   Tracing can be enabled via the slab_debug=T,<slabcache> option
   during boot. SLUB will then protocol all actions on that slabcache
   and dump the object contents on free.

K. On demand DMA cache creation.

   Generally DMA caches are not needed. If a kmalloc is used with
   __GFP_DMA then just create this single slabcache that is needed.
   For systems that have no ZONE_DMA requirement the support is
   completely eliminated.

L. Performance increase

   Some benchmarks have shown speed improvements on kernbench in the
   range of 5-10%. The locking overhead of slub is based on the
   underlying base allocation size. If we can reliably allocate
   larger order pages then it is possible to increase slub
   performance much further. The anti-fragmentation patches may
   enable further performance increases.

Tested on:
i386 UP + SMP, x86_64 UP + SMP + NUMA emulation, IA64 NUMA + Simulator

SLUB Boot options

slub_nomerge		Disable merging of slabs
slub_min_order=x	Require a minimum order for slab caches. This
			increases the managed chunk size and therefore
			reduces meta data and locking overhead.
slub_min_objects=x	Mininum objects per slab. Default is 8.
slub_max_order=x	Avoid generating slabs larger than order specified.
slub_debug		Enable all diagnostics for all caches
slub_debug=<options>	Enable selective options for all caches
slub_debug=<o>,<cache>	Enable selective options for a certain set of
			caches

Available Debug options
F		Double Free checking, sanity and resiliency
R		Red zoning
P		Object / padding poisoning
U		Track last free / alloc
T		Trace all allocs / frees (only use for individual slabs).

To use SLUB: Apply this patch and then select SLUB as the default slab
allocator.

[hugh@veritas.com: fix an oops-causing locking error]
[akpm@linux-foundation.org: various stupid cleanups and small fixes]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 201 insertions, 0 deletions

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
new file mode 100644
index 000000000000..30b154ce7289
--- /dev/null
+++ b/include/linux/slub_def.h
@@ -0,0 +1,201 @@
+#ifndef _LINUX_SLUB_DEF_H
+#define _LINUX_SLUB_DEF_H
+
+/*
+ * SLUB : A Slab allocator without object queues.
+ *
+ * (C) 2007 SGI, Christoph Lameter <clameter@sgi.com>
+ */
+#include <linux/types.h>
+#include <linux/gfp.h>
+#include <linux/workqueue.h>
+#include <linux/kobject.h>
+
+struct kmem_cache_node {
+	spinlock_t list_lock;	/* Protect partial list and nr_partial */
+	unsigned long nr_partial;
+	atomic_long_t nr_slabs;
+	struct list_head partial;
+};
+
+/*
+ * Slab cache management.
+ */
+struct kmem_cache {
+	/* Used for retriving partial slabs etc */
+	unsigned long flags;
+	int size;		/* The size of an object including meta data */
+	int objsize;		/* The size of an object without meta data */
+	int offset;		/* Free pointer offset. */
+	unsigned int order;
+
+	/*
+	 * Avoid an extra cache line for UP, SMP and for the node local to
+	 * struct kmem_cache.
+	 */
+	struct kmem_cache_node local_node;
+
+	/* Allocation and freeing of slabs */
+	int objects;		/* Number of objects in slab */
+	int refcount;		/* Refcount for slab cache destroy */
+	void (*ctor)(void *, struct kmem_cache *, unsigned long);
+	void (*dtor)(void *, struct kmem_cache *, unsigned long);
+	int inuse;		/* Offset to metadata */
+	int align;		/* Alignment */
+	const char *name;	/* Name (only for display!) */
+	struct list_head list;	/* List of slab caches */
+	struct kobject kobj;	/* For sysfs */
+
+#ifdef CONFIG_NUMA
+	int defrag_ratio;
+	struct kmem_cache_node *node[MAX_NUMNODES];
+#endif
+	struct page *cpu_slab[NR_CPUS];
+};
+
+/*
+ * Kmalloc subsystem.
+ */
+#define KMALLOC_SHIFT_LOW 3
+
+#ifdef CONFIG_LARGE_ALLOCS
+#define KMALLOC_SHIFT_HIGH 25
+#else
+#if !defined(CONFIG_MMU) || NR_CPUS > 512 || MAX_NUMNODES > 256
+#define KMALLOC_SHIFT_HIGH 20
+#else
+#define KMALLOC_SHIFT_HIGH 18
+#endif
+#endif
+
+/*
+ * We keep the general caches in an array of slab caches that are used for
+ * 2^x bytes of allocations.
+ */
+extern struct kmem_cache kmalloc_caches[KMALLOC_SHIFT_HIGH + 1];
+
+/*
+ * Sorry that the following has to be that ugly but some versions of GCC
+ * have trouble with constant propagation and loops.
+ */
+static inline int kmalloc_index(int size)
+{
+	if (size == 0)
+		return 0;
+	if (size > 64 && size <= 96)
+		return 1;
+	if (size > 128 && size <= 192)
+		return 2;
+	if (size <=          8) return 3;
+	if (size <=         16) return 4;
+	if (size <=         32) return 5;
+	if (size <=         64) return 6;
+	if (size <=        128) return 7;
+	if (size <=        256) return 8;
+	if (size <=        512) return 9;
+	if (size <=       1024) return 10;
+	if (size <=   2 * 1024) return 11;
+	if (size <=   4 * 1024) return 12;
+	if (size <=   8 * 1024) return 13;
+	if (size <=  16 * 1024) return 14;
+	if (size <=  32 * 1024) return 15;
+	if (size <=  64 * 1024) return 16;
+	if (size <= 128 * 1024) return 17;
+	if (size <= 256 * 1024) return 18;
+#if KMALLOC_SHIFT_HIGH > 18
+	if (size <=  512 * 1024) return 19;
+	if (size <= 1024 * 1024) return 20;
+#endif
+#if KMALLOC_SHIFT_HIGH > 20
+	if (size <=  2 * 1024 * 1024) return 21;
+	if (size <=  4 * 1024 * 1024) return 22;
+	if (size <=  8 * 1024 * 1024) return 23;
+	if (size <= 16 * 1024 * 1024) return 24;
+	if (size <= 32 * 1024 * 1024) return 25;
+#endif
+	return -1;
+
+/*
+ * What we really wanted to do and cannot do because of compiler issues is:
+ *	int i;
+ *	for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++)
+ *		if (size <= (1 << i))
+ *			return i;
+ */
+}
+
+/*
+ * Find the slab cache for a given combination of allocation flags and size.
+ *
+ * This ought to end up with a global pointer to the right cache
+ * in kmalloc_caches.
+ */
+static inline struct kmem_cache *kmalloc_slab(size_t size)
+{
+	int index = kmalloc_index(size);
+
+	if (index == 0)
+		return NULL;
+
+	if (index < 0) {
+		/*
+		 * Generate a link failure. Would be great if we could
+		 * do something to stop the compile here.
+		 */
+		extern void __kmalloc_size_too_large(void);
+		__kmalloc_size_too_large();
+	}
+	return &kmalloc_caches[index];
+}
+
+#ifdef CONFIG_ZONE_DMA
+#define SLUB_DMA __GFP_DMA
+#else
+/* Disable DMA functionality */
+#define SLUB_DMA 0
+#endif
+
+static inline void *kmalloc(size_t size, gfp_t flags)
+{
+	if (__builtin_constant_p(size) && !(flags & SLUB_DMA)) {
+		struct kmem_cache *s = kmalloc_slab(size);
+
+		if (!s)
+			return NULL;
+
+		return kmem_cache_alloc(s, flags);
+	} else
+		return __kmalloc(size, flags);
+}
+
+static inline void *kzalloc(size_t size, gfp_t flags)
+{
+	if (__builtin_constant_p(size) && !(flags & SLUB_DMA)) {
+		struct kmem_cache *s = kmalloc_slab(size);
+
+		if (!s)
+			return NULL;
+
+		return kmem_cache_zalloc(s, flags);
+	} else
+		return __kzalloc(size, flags);
+}
+
+#ifdef CONFIG_NUMA
+extern void *__kmalloc_node(size_t size, gfp_t flags, int node);
+
+static inline void *kmalloc_node(size_t size, gfp_t flags, int node)
+{
+	if (__builtin_constant_p(size) && !(flags & SLUB_DMA)) {
+		struct kmem_cache *s = kmalloc_slab(size);
+
+		if (!s)
+			return NULL;
+
+		return kmem_cache_alloc_node(s, flags, node);
+	} else
+		return __kmalloc_node(size, flags, node);
+}
+#endif
+
+#endif /* _LINUX_SLUB_DEF_H */