[PATCH] slob: introduce the SLOB allocator

configurable replacement for slab allocator

This adds a CONFIG_SLAB option under CONFIG_EMBEDDED.  When CONFIG_SLAB is
disabled, the kernel falls back to using the 'SLOB' allocator.

SLOB is a traditional K&R/UNIX allocator with a SLAB emulation layer,
similar to the original Linux kmalloc allocator that SLAB replaced.  It's
signicantly smaller code and is more memory efficient.  But like all
similar allocators, it scales poorly and suffers from fragmentation more
than SLAB, so it's only appropriate for small systems.

It's been tested extensively in the Linux-tiny tree.  I've also
stress-tested it with make -j 8 compiles on a 3G SMP+PREEMPT box (not
recommended).

Here's a comparison for otherwise identical builds, showing SLOB saving
nearly half a megabyte of RAM:

$ size vmlinux*
   text    data     bss     dec     hex filename
3336372  529360  190812 4056544  3de5e0 vmlinux-slab
3323208  527948  190684 4041840  3dac70 vmlinux-slob

$ size mm/{slab,slob}.o
   text    data     bss     dec     hex filename
  13221     752      48   14021    36c5 mm/slab.o
   1896      52       8    1956     7a4 mm/slob.o

/proc/meminfo:
                  SLAB          SLOB      delta
MemTotal:        27964 kB      27980 kB     +16 kB
MemFree:         24596 kB      25092 kB    +496 kB
Buffers:            36 kB         36 kB       0 kB
Cached:           1188 kB       1188 kB       0 kB
SwapCached:          0 kB          0 kB       0 kB
Active:            608 kB        600 kB      -8 kB
Inactive:          808 kB        812 kB      +4 kB
HighTotal:           0 kB          0 kB       0 kB
HighFree:            0 kB          0 kB       0 kB
LowTotal:        27964 kB      27980 kB     +16 kB
LowFree:         24596 kB      25092 kB    +496 kB
SwapTotal:           0 kB          0 kB       0 kB
SwapFree:            0 kB          0 kB       0 kB
Dirty:               4 kB         12 kB      +8 kB
Writeback:           0 kB          0 kB       0 kB
Mapped:            560 kB        556 kB      -4 kB
Slab:             1756 kB          0 kB   -1756 kB
CommitLimit:     13980 kB      13988 kB      +8 kB
Committed_AS:     4208 kB       4208 kB       0 kB
PageTables:         28 kB         28 kB       0 kB
VmallocTotal:  1007312 kB    1007312 kB       0 kB
VmallocUsed:        48 kB         48 kB       0 kB
VmallocChunk:  1007264 kB    1007264 kB       0 kB

(this work has been sponsored in part by CELF)

From: Ingo Molnar <[email protected]>

   Fix 32-bitness bugs in mm/slob.c.

Signed-off-by: Matt Mackall <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/proc/proc_misc.c

@@ -323,6 +323,7 @@ static struct file_operations proc_modules_operations = {
 };
 #endif
 
+#ifdef CONFIG_SLAB
 extern struct seq_operations slabinfo_op;
 extern ssize_t slabinfo_write(struct file *, const char __user *, size_t, loff_t *);
 static int slabinfo_open(struct inode *inode, struct file *file)
@@ -336,6 +337,7 @@ static struct file_operations proc_slabinfo_operations = {
 	.llseek		= seq_lseek,
 	.release	= seq_release,
 };
+#endif
 
 static int show_stat(struct seq_file *p, void *v)
 {
@@ -600,7 +602,9 @@ void __init proc_misc_init(void)
 	create_seq_entry("partitions", 0, &proc_partitions_operations);
 	create_seq_entry("stat", 0, &proc_stat_operations);
 	create_seq_entry("interrupts", 0, &proc_interrupts_operations);
+#ifdef CONFIG_SLAB
 	create_seq_entry("slabinfo",S_IWUSR|S_IRUGO,&proc_slabinfo_operations);
+#endif
 	create_seq_entry("buddyinfo",S_IRUGO, &fragmentation_file_operations);
 	create_seq_entry("vmstat",S_IRUGO, &proc_vmstat_file_operations);
 	create_seq_entry("zoneinfo",S_IRUGO, &proc_zoneinfo_file_operations);

include/linux/slab.h

@@ -53,6 +53,8 @@ typedef struct kmem_cache kmem_cache_t;
 #define SLAB_CTOR_ATOMIC	0x002UL		/* tell constructor it can't sleep */
 #define	SLAB_CTOR_VERIFY	0x004UL		/* tell constructor it's a verify call */
 
+#ifndef CONFIG_SLOB
+
 /* prototypes */
 extern void __init kmem_cache_init(void);
 
@@ -134,6 +136,39 @@ static inline void *kmalloc_node(size_t size, gfp_t flags, int node)
 extern int FASTCALL(kmem_cache_reap(int));
 extern int FASTCALL(kmem_ptr_validate(kmem_cache_t *cachep, void *ptr));
 
+#else /* CONFIG_SLOB */
+
+/* SLOB allocator routines */
+
+void kmem_cache_init(void);
+struct kmem_cache *kmem_find_general_cachep(size_t, gfp_t gfpflags);
+struct kmem_cache *kmem_cache_create(const char *c, size_t, size_t,
+	unsigned long,
+	void (*)(void *, struct kmem_cache *, unsigned long),
+	void (*)(void *, struct kmem_cache *, unsigned long));
+int kmem_cache_destroy(struct kmem_cache *c);
+void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags);
+void kmem_cache_free(struct kmem_cache *c, void *b);
+const char *kmem_cache_name(struct kmem_cache *);
+void *kmalloc(size_t size, gfp_t flags);
+void *kzalloc(size_t size, gfp_t flags);
+void kfree(const void *m);
+unsigned int ksize(const void *m);
+unsigned int kmem_cache_size(struct kmem_cache *c);
+
+static inline void *kcalloc(size_t n, size_t size, gfp_t flags)
+{
+	return kzalloc(n * size, flags);
+}
+
+#define kmem_cache_shrink(d) (0)
+#define kmem_cache_reap(a)
+#define kmem_ptr_validate(a, b) (0)
+#define kmem_cache_alloc_node(c, f, n) kmem_cache_alloc(c, f)
+#define kmalloc_node(s, f, n) kmalloc(s, f)
+
+#endif /* CONFIG_SLOB */
+
 /* System wide caches */
 extern kmem_cache_t	*vm_area_cachep;
 extern kmem_cache_t	*names_cachep;

init/Kconfig

@@ -380,6 +380,15 @@ config CC_ALIGN_JUMPS
 	  no dummy operations need be executed.
 	  Zero means use compiler's default.
 
+config SLAB
+	default y
+	bool "Use full SLAB allocator" if EMBEDDED
+	help
+	  Disabling this replaces the advanced SLAB allocator and
+	  kmalloc support with the drastically simpler SLOB allocator.
+	  SLOB is more space efficient but does not scale well and is
+	  more susceptible to fragmentation.
+
 endmenu		# General setup
 
 config TINY_SHMEM
@@ -391,6 +400,10 @@ config BASE_SMALL
 	default 0 if BASE_FULL
 	default 1 if !BASE_FULL
 
+config SLOB
+	default !SLAB
+	bool
+
 menu "Loadable module support"
 
 config MODULES

mm/Makefile

@@ -9,7 +9,7 @@ mmu-$(CONFIG_MMU)	:= fremap.o highmem.o madvise.o memory.o mincore.o \
 
 obj-y			:= bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
 			   page_alloc.o page-writeback.o pdflush.o \
-			   readahead.o slab.o swap.o truncate.o vmscan.o \
+			   readahead.o swap.o truncate.o vmscan.o \
 			   prio_tree.o util.o $(mmu-y)
 
 obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o thrash.o
@@ -18,5 +18,7 @@ obj-$(CONFIG_NUMA) 	+= mempolicy.o
 obj-$(CONFIG_SPARSEMEM)	+= sparse.o
 obj-$(CONFIG_SHMEM) += shmem.o
 obj-$(CONFIG_TINY_SHMEM) += tiny-shmem.o
+obj-$(CONFIG_SLOB) += slob.o
+obj-$(CONFIG_SLAB) += slab.o
 obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
 obj-$(CONFIG_FS_XIP) += filemap_xip.o