[patch] slab: add memory hotplug support

[David Rientjes]

Slab lacks any memory hotplug support for nodes that are hotplugged
without cpus being hotplugged.  This is possible at least on x86
CONFIG_MEMORY_HOTPLUG_SPARSE kernels where SRAT entries are marked
ACPI_SRAT_MEM_HOT_PLUGGABLE and the regions of RAM represent a seperate
node.  It can also be done manually by writing the start address to
/sys/devices/system/memory/probe for kernels that have
CONFIG_ARCH_MEMORY_PROBE set, which is how this patch was tested, and
then onlining the new memory region.

When a node is hotadded, a nodelist for that node is allocated and 
initialized for each slab cache.  If this isn't completed due to a lack
of memory, the hotadd is aborted: we have a reasonable expectation that
kmalloc_node(nid) will work for all caches if nid is online and memory is
available.  

Since nodelists must be allocated and initialized prior to the new node's
memory actually being online, the struct kmem_list3 is allocated off-node
due to kmalloc_node()'s fallback.

When an entire node is offlined (or an online is aborted), these
nodelists are subsequently drained and freed.  If objects still exist
either on the partial or full lists for those nodes, the offline is
aborted.  This scenario will not occur for an aborted online, however,
since objects can never be allocated from those nodelists until the
online has completed.

Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 mm/slab.c |  202 +++++++++++++++++++++++++++++++++++++++++++++++++++----------
 1 files changed, 170 insertions(+), 32 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -115,6 +115,7 @@
 #include	<linux/reciprocal_div.h>
 #include	<linux/debugobjects.h>
 #include	<linux/kmemcheck.h>
+#include	<linux/memory.h>
 
 #include	<asm/cacheflush.h>
 #include	<asm/tlbflush.h>
@@ -1105,6 +1106,52 @@ static inline int cache_free_alien(struct kmem_cache *cachep, void *objp)
 }
 #endif
 
+/*
+ * Allocates and initializes nodelists for a node on each slab cache, used for
+ * either memory or cpu hotplug.  If memory is being hot-added, the kmem_list3
+ * will be allocated off-node since memory is not yet online for the new node.
+ * When hotplugging memory or a cpu, existing nodelists are not replaced if
+ * already in use.
+ *
+ * Must hold cache_chain_mutex.
+ */
+static int init_cache_nodelists_node(int node)
+{
+	struct kmem_cache *cachep;
+	struct kmem_list3 *l3;
+	const int memsize = sizeof(struct kmem_list3);
+
+	list_for_each_entry(cachep, &cache_chain, next) {
+		/*
+		 * Set up the size64 kmemlist for cpu before we can
+		 * begin anything. Make sure some other cpu on this
+		 * node has not already allocated this
+		 */
+		if (!cachep->nodelists[node]) {
+			l3 = kmalloc_node(memsize, GFP_KERNEL, node);
+			if (!l3)
+				return -ENOMEM;
+			kmem_list3_init(l3);
+			l3->next_reap = jiffies + REAPTIMEOUT_LIST3 +
+			    ((unsigned long)cachep) % REAPTIMEOUT_LIST3;
+
+			/*
+			 * The l3s don't come and go as CPUs come and
+			 * go.  cache_chain_mutex is sufficient
+			 * protection here.
+			 */
+			cachep->nodelists[node] = l3;
+		}
+
+		spin_lock_irq(&cachep->nodelists[node]->list_lock);
+		cachep->nodelists[node]->free_limit =
+			(1 + nr_cpus_node(node)) *
+			cachep->batchcount + cachep->num;
+		spin_unlock_irq(&cachep->nodelists[node]->list_lock);
+	}
+	return 0;
+}
+
 static void __cpuinit cpuup_canceled(long cpu)
 {
 	struct kmem_cache *cachep;
@@ -1175,7 +1222,7 @@ static int __cpuinit cpuup_prepare(long cpu)
 	struct kmem_cache *cachep;
 	struct kmem_list3 *l3 = NULL;
 	int node = cpu_to_node(cpu);
-	const int memsize = sizeof(struct kmem_list3);
+	int err;
 
 	/*
 	 * We need to do this right in the beginning since
@@ -1183,35 +1230,9 @@ static int __cpuinit cpuup_prepare(long cpu)
 	 * kmalloc_node allows us to add the slab to the right
 	 * kmem_list3 and not this cpu's kmem_list3
 	 */
-
-	list_for_each_entry(cachep, &cache_chain, next) {
-		/*
-		 * Set up the size64 kmemlist for cpu before we can
-		 * begin anything. Make sure some other cpu on this
-		 * node has not already allocated this
-		 */
-		if (!cachep->nodelists[node]) {
-			l3 = kmalloc_node(memsize, GFP_KERNEL, node);
-			if (!l3)
-				goto bad;
-			kmem_list3_init(l3);
-			l3->next_reap = jiffies + REAPTIMEOUT_LIST3 +
-			    ((unsigned long)cachep) % REAPTIMEOUT_LIST3;
-
-			/*
-			 * The l3s don't come and go as CPUs come and
-			 * go.  cache_chain_mutex is sufficient
-			 * protection here.
-			 */
-			cachep->nodelists[node] = l3;
-		}
-
-		spin_lock_irq(&cachep->nodelists[node]->list_lock);
-		cachep->nodelists[node]->free_limit =
-			(1 + nr_cpus_node(node)) *
-			cachep->batchcount + cachep->num;
-		spin_unlock_irq(&cachep->nodelists[node]->list_lock);
-	}
+	err = init_cache_nodelists_node(node);
+	if (err < 0)
+		goto bad;
 
 	/*
 	 * Now we can go ahead with allocating the shared arrays and
@@ -1334,11 +1355,120 @@ static struct notifier_block __cpuinitdata cpucache_notifier = {
 	&cpuup_callback, NULL, 0
 };
 
+#if defined(CONFIG_NUMA) && defined(CONFIG_MEMORY_HOTPLUG)
+/*
+ * Drains and frees nodelists for a node on each slab cache, used for memory
+ * hotplug.  Returns -EBUSY if all objects cannot be drained on memory
+ * hot-remove so that the node is not removed.  When used because memory
+ * hot-add is canceled, the only result is the freed kmem_list3.
+ *
+ * Must hold cache_chain_mutex.
+ */
+static int __meminit free_cache_nodelists_node(int node)
+{
+	struct kmem_cache *cachep;
+	int ret = 0;
+
+	list_for_each_entry(cachep, &cache_chain, next) {
+		struct array_cache *shared;
+		struct array_cache **alien;
+		struct kmem_list3 *l3;
+
+		l3 = cachep->nodelists[node];
+		if (!l3)
+			continue;
+
+		spin_lock_irq(&l3->list_lock);
+		shared = l3->shared;
+		if (shared) {
+			free_block(cachep, shared->entry, shared->avail, node);
+			l3->shared = NULL;
+		}
+		alien = l3->alien;
+		l3->alien = NULL;
+		spin_unlock_irq(&l3->list_lock);
+
+		if (alien) {
+			drain_alien_cache(cachep, alien);
+			free_alien_cache(alien);
+		}
+		kfree(shared);
+
+		drain_freelist(cachep, l3, l3->free_objects);
+		if (!list_empty(&l3->slabs_full) ||
+					!list_empty(&l3->slabs_partial)) {
+			/*
+			 * Continue to iterate through each slab cache to free
+			 * as many nodelists as possible even though the
+			 * offline will be canceled.
+			 */
+			ret = -EBUSY;
+			continue;
+		}
+		kfree(l3);
+		cachep->nodelists[node] = NULL;
+	}
+	return ret;
+}
+
+/*
+ * Onlines nid either as the result of memory hot-add or canceled hot-remove.
+ */
+static int __meminit slab_node_online(int nid)
+{
+	int ret;
+	mutex_lock(&cache_chain_mutex);
+	ret = init_cache_nodelists_node(nid);
+	mutex_unlock(&cache_chain_mutex);
+	return ret;
+}
+
+/*
+ * Offlines nid either as the result of memory hot-remove or canceled hot-add.
+ */
+static int __meminit slab_node_offline(int nid)
+{
+	int ret;
+	mutex_lock(&cache_chain_mutex);
+	ret = free_cache_nodelists_node(nid);
+	mutex_unlock(&cache_chain_mutex);
+	return ret;
+}
+
+static int __meminit slab_memory_callback(struct notifier_block *self,
+					unsigned long action, void *arg)
+{
+	struct memory_notify *mnb = arg;
+	int ret = 0;
+	int nid;
+
+	nid = mnb->status_change_nid;
+	if (nid < 0)
+		goto out;
+
+	switch (action) {
+	case MEM_GOING_ONLINE:
+	case MEM_CANCEL_OFFLINE:
+		ret = slab_node_online(nid);
+		break;
+	case MEM_GOING_OFFLINE:
+	case MEM_CANCEL_ONLINE:
+		ret = slab_node_offline(nid);
+		break;
+	case MEM_ONLINE:
+	case MEM_OFFLINE:
+		break;
+	}
+out:
+	return ret ? notifier_from_errno(ret) : NOTIFY_OK;
+}
+#endif /* CONFIG_NUMA && CONFIG_MEMORY_HOTPLUG */
+
 /*
  * swap the static kmem_list3 with kmalloced memory
  */
-static void init_list(struct kmem_cache *cachep, struct kmem_list3 *list,
-			int nodeid)
+static void __init init_list(struct kmem_cache *cachep, struct kmem_list3 *list,
+				int nodeid)
 {
 	struct kmem_list3 *ptr;
 
@@ -1583,6 +1713,14 @@ void __init kmem_cache_init_late(void)
 	 */
 	register_cpu_notifier(&cpucache_notifier);
 
+#ifdef CONFIG_NUMA
+	/*
+	 * Register a memory hotplug callback that initializes and frees
+	 * nodelists.
+	 */
+	hotplug_memory_notifier(slab_memory_callback, SLAB_CALLBACK_PRI);
+#endif
+
 	/*
 	 * The reap timers are started later, with a module init call: That part
 	 * of the kernel is not yet operational.
--
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