[PATCH] slab: initialisation cleanup and oops fix

From: Manfred Spraul <manfred@colorfullife.com>

attached is the promised cleanup/bugfix patch for the slab bootstrap:

- kmem_cache_init & kmem_cache_sizes_init merged into one function,
  called after mem_init().  It's impossible to bring slab to an operational
  state without working gfp, thus the early partial initialization is not
  necessary.

- g_cpucache_up set to FULL at the end of kmem_cache_init instead of the
  module init call.  This is a bugfix: slab was completely initialized,
  just the update of the state was missing.

- some documentation for the bootstrap added.

The minimal fix for the bug is a two-liner: move g_cpucache_up=FULL from
cpucache_init to kmem_cache_sizes_init, but I want to get rid of
kmem_cache_sizes_init, too.

include/linux/slab.h

@@ -49,7 +49,6 @@ typedef struct kmem_cache_s kmem_cache_t;
 
 /* prototypes */
 extern void kmem_cache_init(void);
-extern void kmem_cache_sizes_init(void);
 
 extern kmem_cache_t *kmem_find_general_cachep(size_t, int gfpflags);
 extern kmem_cache_t *kmem_cache_create(const char *, size_t, size_t, unsigned long,

init/main.c

@@ -417,7 +417,6 @@ asmlinkage void __init start_kernel(void)
 	 */
 	console_init();
 	profile_init();
-	kmem_cache_init();
 	local_irq_enable();
 	calibrate_delay();
 #ifdef CONFIG_BLK_DEV_INITRD
@@ -430,7 +429,7 @@ asmlinkage void __init start_kernel(void)
 #endif
 	page_address_init();
 	mem_init();
-	kmem_cache_sizes_init();
+	kmem_cache_init();
 	pidmap_init();
 	pgtable_cache_init();
 	pte_chain_init();

mm/slab.c

@@ -567,11 +567,40 @@ static inline struct array_cache *ac_data(kmem_cache_t *cachep)
 	return cachep->array[smp_processor_id()];
 }
 
-/* Initialisation - setup the `cache' cache. */
+/* Initialisation.
+ * Called after the gfp() functions have been enabled, and before smp_init().
+ */
 void __init kmem_cache_init(void)
 {
 	size_t left_over;
+	struct cache_sizes *sizes;
+	struct cache_names *names;
+
+	/*
+	 * Fragmentation resistance on low memory - only use bigger
+	 * page orders on machines with more than 32MB of memory.
+	 */
+	if (num_physpages > (32 << 20) >> PAGE_SHIFT)
+		slab_break_gfp_order = BREAK_GFP_ORDER_HI;
 
+	
+	/* Bootstrap is tricky, because several objects are allocated
+	 * from caches that do not exist yet:
+	 * 1) initialize the cache_cache cache: it contains the kmem_cache_t
+	 *    structures of all caches, except cache_cache itself: cache_cache
+	 *    is statically allocated.
+	 *    Initially an __init data area is used for the head array, it's
+	 *    replaced with a kmalloc allocated array at the end of the bootstrap.
+	 * 2) Create the first kmalloc cache.
+	 *    The kmem_cache_t for the new cache is allocated normally. An __init
+	 *    data area is used for the head array.
+	 * 3) Create the remaining kmalloc caches, with minimally sized head arrays.
+	 * 4) Replace the __init data head arrays for cache_cache and the first
+	 *    kmalloc cache with kmalloc allocated arrays.
+	 * 5) Resize the head arrays of the kmalloc caches to their final sizes.
+	 */
+
+	/* 1) create the cache_cache */
 	init_MUTEX(&cache_chain_sem);
 	INIT_LIST_HEAD(&cache_chain);
 	list_add(&cache_cache.next, &cache_chain);
@@ -585,27 +614,10 @@ void __init kmem_cache_init(void)
 	cache_cache.colour = left_over/cache_cache.colour_off;
 	cache_cache.colour_next = 0;
 
-	/* Register a cpu startup notifier callback
-	 * that initializes ac_data for all new cpus
-	 */
-	register_cpu_notifier(&cpucache_notifier);
-}
-
 
-/* Initialisation - setup remaining internal and general caches.
- * Called after the gfp() functions have been enabled, and before smp_init().
- */
-void __init kmem_cache_sizes_init(void)
-{
-	struct cache_sizes *sizes = malloc_sizes;
-	struct cache_names *names = cache_names;
-
-	/*
-	 * Fragmentation resistance on low memory - only use bigger
-	 * page orders on machines with more than 32MB of memory.
-	 */
-	if (num_physpages > (32 << 20) >> PAGE_SHIFT)
-		slab_break_gfp_order = BREAK_GFP_ORDER_HI;
+	/* 2+3) create the kmalloc caches */
+	sizes = malloc_sizes;
+	names = cache_names;
 
 	while (sizes->cs_size) {
 		/* For performance, all the general caches are L1 aligned.
@@ -634,10 +646,7 @@ void __init kmem_cache_sizes_init(void)
 		sizes++;
 		names++;
 	}
-	/*
-	 * The generic caches are running - time to kick out the
-	 * bootstrap cpucaches.
-	 */
+	/* 4) Replace the bootstrap head arrays */
 	{
 		void * ptr;
 		
@@ -656,29 +665,42 @@ void __init kmem_cache_sizes_init(void)
 		malloc_sizes[0].cs_cachep->array[smp_processor_id()] = ptr;
 		local_irq_enable();
 	}
+
+	/* 5) resize the head arrays to their final sizes */
+	{
+		kmem_cache_t *cachep;
+		down(&cache_chain_sem);
+		list_for_each_entry(cachep, &cache_chain, next)
+			enable_cpucache(cachep);
+		up(&cache_chain_sem);
+	}
+
+	/* Done! */
+	g_cpucache_up = FULL;
+
+	/* Register a cpu startup notifier callback
+	 * that initializes ac_data for all new cpus
+	 */
+	register_cpu_notifier(&cpucache_notifier);
+	
+
+	/* The reap timers are started later, with a module init call:
+	 * That part of the kernel is not yet operational.
+	 */
 }
 
 int __init cpucache_init(void)
 {
-	kmem_cache_t *cachep;
 	int cpu;
 
-	down(&cache_chain_sem);
-	g_cpucache_up = FULL;
-
-	list_for_each_entry(cachep, &cache_chain, next)
-		enable_cpucache(cachep);
-	
 	/* 
 	 * Register the timers that return unneeded
 	 * pages to gfp.
 	 */
-
 	for (cpu = 0; cpu < NR_CPUS; cpu++) {
 		if (cpu_online(cpu))
 			start_cpu_timer(cpu);
 	}
-	up(&cache_chain_sem);
 
 	return 0;
 }