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Subject[Patch 002/002] Create/delete kmem_cache_node for SLUB on memory online callback

This is to make kmem_cache_nodes of all SLUBs for new node when
memory-hotadd is called. This fixes panic due to access NULL pointer at
discard_slab() after memory hot-add.

If pages on the new node available, slub can use it before making
new kmem_cache_nodes. So, this callback should be called
BEFORE pages on the node are available.

When memory online is called, slab_mem_going_online_callback() is
called to make kmem_cache_node(). if it (or other callbacks) fails,
then slab_mem_offline_callback() is called for rollback.

In memory offline, slab_mem_going_offline_callback() is called to
shrink cache, then slab_mem_offline_callback() is called later.


Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>

---
mm/slub.c | 117 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 117 insertions(+)

Index: current/mm/slub.c
===================================================================
--- current.orig/mm/slub.c 2007-10-11 20:31:37.000000000 +0900
+++ current/mm/slub.c 2007-10-11 21:58:10.000000000 +0900
@@ -20,6 +20,7 @@
#include <linux/mempolicy.h>
#include <linux/ctype.h>
#include <linux/kallsyms.h>
+#include <linux/memory.h>

/*
* Lock order:
@@ -2711,6 +2712,120 @@ int kmem_cache_shrink(struct kmem_cache
}
EXPORT_SYMBOL(kmem_cache_shrink);

+#if defined(CONFIG_NUMA) && defined(CONFIG_MEMORY_HOTPLUG)
+static int slab_mem_going_offline_callback(void *arg)
+{
+ struct kmem_cache *s;
+ struct memory_notify *marg = arg;
+ int local_node, offline_node = marg->status_change_nid;
+
+ if (offline_node < 0)
+ /* node has memory yet. nothing to do. */
+ return 0;
+
+ down_read(&slub_lock);
+ list_for_each_entry(s, &slab_caches, list) {
+ local_node = page_to_nid(virt_to_page(s));
+ if (local_node == offline_node)
+ /* This slub is on the offline node. */
+ return -EBUSY;
+ }
+ up_read(&slub_lock);
+
+ kmem_cache_shrink_node(s, offline_node);
+
+ return 0;
+}
+
+static void slab_mem_offline_callback(void *arg)
+{
+ struct kmem_cache_node *n;
+ struct kmem_cache *s;
+ struct memory_notify *marg = arg;
+ int offline_node;
+
+ offline_node = marg->status_change_nid;
+
+ if (offline_node < 0)
+ /* node has memory yet. nothing to do. */
+ return;
+
+ down_read(&slub_lock);
+ list_for_each_entry(s, &slab_caches, list) {
+ n = get_node(s, offline_node);
+ if (n) {
+ /*
+ * if n->nr_slabs > 0, offline_pages() must be fail,
+ * because the node is used by slub yet.
+ */
+ BUG_ON(atomic_read(&n->nr_slabs));
+
+ s->node[offline_node] = NULL;
+ kmem_cache_free(kmalloc_caches, n);
+ }
+ }
+ up_read(&slub_lock);
+}
+
+static int slab_mem_going_online_callback(void *arg)
+{
+ struct kmem_cache_node *n;
+ struct kmem_cache *s;
+ struct memory_notify *marg = arg;
+ int nid = marg->status_change_nid;
+
+ /* If the node already has memory, then nothing is necessary. */
+ if (nid < 0)
+ return 0;
+
+ /*
+ * New memory will be onlined on the node which has no memory so far.
+ * New kmem_cache_node is necssary for it.
+ */
+ down_read(&slub_lock);
+ list_for_each_entry(s, &slab_caches, list) {
+ /*
+ * XXX: The new node's memory can't be allocated yet,
+ * kmem_cache_node will be allocated other node.
+ */
+ n = kmem_cache_alloc(kmalloc_caches, GFP_KERNEL);
+ if (!n)
+ return -ENOMEM;
+ init_kmem_cache_node(n);
+ s->node[nid] = n;
+ }
+ up_read(&slub_lock);
+
+ return 0;
+}
+
+static int slab_memory_callback(struct notifier_block *self,
+ unsigned long action, void *arg)
+{
+ int ret = 0;
+
+ switch (action) {
+ case MEM_GOING_ONLINE:
+ ret = slab_mem_going_online_callback(arg);
+ break;
+ case MEM_GOING_OFFLINE:
+ ret = slab_mem_going_offline_callback(arg);
+ break;
+ case MEM_OFFLINE:
+ case MEM_CANCEL_ONLINE:
+ slab_mem_offline_callback(arg);
+ break;
+ case MEM_ONLINE:
+ case MEM_CANCEL_OFFLINE:
+ break;
+ }
+
+ ret = notifier_from_errno(ret);
+ return ret;
+}
+
+#endif /* CONFIG_MEMORY_HOTPLUG */
+
/********************************************************************
* Basic setup of slabs
*******************************************************************/
@@ -2741,6 +2856,8 @@ void __init kmem_cache_init(void)
sizeof(struct kmem_cache_node), GFP_KERNEL);
kmalloc_caches[0].refcount = -1;
caches++;
+
+ hotplug_memory_notifier(slab_memory_callback, 1);
#endif

/* Able to allocate the per node structures */
--
Yasunori Goto


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