[PATCH] Show slab memory usage on OOM and SysRq-M

[Pavel Emelianov]

The out_of_memory() function and SysRq-M handler call
show_mem() to show the current memory usage state.

This is also helpful to see which slabs are the largest
in the system.

Signed-off-by: Pavel Emelianov <xemul@xxxxxxxxxx>
Signed-off-by: Kirill Korotaev <dev@xxxxxxxxxx>

---

diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 39cc318..7c27647 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -234,6 +234,7 @@ static struct sysrq_key_op sysrq_showsta
 static void sysrq_handle_showmem(int key, struct tty_struct *tty)
 {
 	show_mem();
+	show_slabs();
 }
 static struct sysrq_key_op sysrq_showmem_op = {
 	.handler	= sysrq_handle_showmem,
diff --git a/include/linux/mm.h b/include/linux/mm.h
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 67425c2..1e2919d 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -170,6 +170,12 @@ static inline void *kzalloc(size_t size,
 }
 #endif
 
+#ifdef CONFIG_SLAB
+extern void show_slabs(void);
+#else
+#define show_slabs(void)	do { } while (0)
+#endif
+
 #ifndef CONFIG_NUMA
 static inline void *kmalloc_node(size_t size, gfp_t flags, int node)
 {
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 4bdc7c0..aefdd06 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -409,6 +409,7 @@ void out_of_memory(struct zonelist *zone
 			current->comm, gfp_mask, order, current->oomkilladj);
 		dump_stack();
 		show_mem();
+		show_slabs();
 	}
 
 	cpuset_lock();
diff --git a/mm/slab.c b/mm/slab.c
index 21b3c61..9a5829a 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -749,6 +749,7 @@ static inline void init_lock_keys(void)
  * 2. Protect sanity of cpu_online_map against cpu hotplug events
  */
 static DEFINE_MUTEX(cache_chain_mutex);
+static DEFINE_SPINLOCK(cache_chain_lock);
 static struct list_head cache_chain;
 
 /*
@@ -2377,7 +2378,9 @@ kmem_cache_create (const char *name, siz
 	}
 
 	/* cache setup completed, link it into the list */
+	spin_lock_irq(&cache_chain_lock);
 	list_add(&cachep->next, &cache_chain);
+	spin_unlock_irq(&cache_chain_lock);
 oops:
 	if (!cachep && (flags & SLAB_PANIC))
 		panic("kmem_cache_create(): failed to create slab `%s'\n",
@@ -2566,10 +2569,14 @@ void kmem_cache_destroy(struct kmem_cach
 	/*
 	 * the chain is never empty, cache_cache is never destroyed
 	 */
+	spin_lock_irq(&cache_chain_lock);
 	list_del(&cachep->next);
+	spin_unlock_irq(&cache_chain_lock);
 	if (__cache_shrink(cachep)) {
 		slab_error(cachep, "Can't free all objects");
+		spin_lock_irq(&cache_chain_lock);
 		list_add(&cachep->next, &cache_chain);
+		spin_unlock_irq(&cache_chain_lock);
 		mutex_unlock(&cache_chain_mutex);
 		return;
 	}
@@ -4543,6 +4550,73 @@ const struct seq_operations slabstats_op
 #endif
 #endif
 
+#define SHOW_TOP_SLABS 10
+
+static unsigned long get_cache_size(struct kmem_cache *cachep)
+{
+	unsigned long slabs;
+	struct kmem_list3 *l3;
+	struct list_head *lh;
+	int node;
+
+	slabs = 0;
+
+	for_each_online_node (node) {
+		l3 = cachep->nodelists[node];
+		if (l3 == NULL)
+			continue;
+
+		spin_lock(&l3->list_lock);
+		list_for_each (lh, &l3->slabs_full)
+			slabs++;
+		list_for_each (lh, &l3->slabs_partial)
+			slabs++;
+		list_for_each (lh, &l3->slabs_free)
+			slabs++;
+		spin_unlock(&l3->list_lock);
+	}
+
+	return slabs * ((PAGE_SIZE << cachep->gfporder) +
+		(OFF_SLAB(cachep) ? cachep->slabp_cache->buffer_size : 0));
+}
+
+void show_slabs(void)
+{
+	int i, j;
+	unsigned long size;
+	struct kmem_cache *ptr;
+	unsigned long sizes[SHOW_TOP_SLABS];
+	struct kmem_cache *top[SHOW_TOP_SLABS];
+	unsigned long flags;
+
+	printk("Top %d caches:\n", SHOW_TOP_SLABS);
+	memset(top, 0, sizeof(top));
+	memset(sizes, 0, sizeof(sizes));
+
+	spin_lock_irqsave(&cache_chain_lock, flags);
+	list_for_each_entry (ptr, &cache_chain, next) {
+		size = get_cache_size(ptr);
+
+		/* find and replace the smallest size seen so far */
+		j = 0;
+		for (i = 1; i < SHOW_TOP_SLABS; i++)
+			if (sizes[i] < sizes[j])
+				j = i;
+
+		if (size > sizes[j]) {
+			sizes[j] = size;
+			top[j] = ptr;
+		}
+	}
+
+	for (i = 0; i < SHOW_TOP_SLABS; i++)
+		if (top[i])
+			printk("%-21s: size %10lu objsize %10u\n",
+					top[i]->name, sizes[i],
+					top[i]->buffer_size);
+	spin_unlock_irqrestore(&cache_chain_lock, flags);
+}
+
 /**
  * ksize - get the actual amount of memory allocated for a given object
  * @objp: Pointer to the object
-
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