[PATCH] sparsemem extreme: hotplug preparation

This splits up sparse_index_alloc() into two pieces.  This is needed
because we'll allocate the memory for the second level in a different place
from where we actually consume it to keep the allocation from happening
underneath a lock

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Bob Picco <bob.picco@hp.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 42 insertions, 12 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 79cf578e21b9..5ed471b58f4f 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -588,6 +588,7 @@ static inline int pfn_valid(unsigned long pfn)
 void sparse_init(void);
 #else
 #define sparse_init()   do {} while (0)
+#define sparse_index_init(_sec, _nid)  do {} while (0)
 #endif /* CONFIG_SPARSEMEM */
 
 #ifdef CONFIG_NODES_SPAN_OTHER_NODES
diff --git a/mm/sparse.c b/mm/sparse.c
index fa01292157a9..347249a4917a 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -6,6 +6,7 @@
 #include <linux/mmzone.h>
 #include <linux/bootmem.h>
 #include <linux/module.h>
+#include <linux/spinlock.h>
 #include <asm/dma.h>
 
 /*
@@ -22,27 +23,55 @@ struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]
 #endif
 EXPORT_SYMBOL(mem_section);
 
-static void sparse_alloc_root(unsigned long root, int nid)
-{
 #ifdef CONFIG_SPARSEMEM_EXTREME
-        mem_section[root] = alloc_bootmem_node(NODE_DATA(nid), PAGE_SIZE);
-#endif
+static struct mem_section *sparse_index_alloc(int nid)
+{
+        struct mem_section *section = NULL;
+        unsigned long array_size = SECTIONS_PER_ROOT *
+                                   sizeof(struct mem_section);
+
+        section = alloc_bootmem_node(NODE_DATA(nid), array_size);
+
+        if (section)
+                memset(section, 0, array_size);
+
+        return section;
 }
 
-static void sparse_index_init(unsigned long section, int nid)
+static int sparse_index_init(unsigned long section_nr, int nid)
 {
-        unsigned long root = SECTION_NR_TO_ROOT(section);
+        static spinlock_t index_init_lock = SPIN_LOCK_UNLOCKED;
+        unsigned long root = SECTION_NR_TO_ROOT(section_nr);
+        struct mem_section *section;
+        int ret = 0;
 
         if (mem_section[root])
-                return;
+                return -EEXIST;
 
-        sparse_alloc_root(root, nid);
+        section = sparse_index_alloc(nid);
+        /*
+         * This lock keeps two different sections from
+         * reallocating for the same index
+         */
+        spin_lock(&index_init_lock);
 
-        if (mem_section[root])
-                memset(mem_section[root], 0, PAGE_SIZE);
-        else
-                panic("memory_present: NO MEMORY\n");
+        if (mem_section[root]) {
+                ret = -EEXIST;
+                goto out;
+        }
+
+        mem_section[root] = section;
+out:
+        spin_unlock(&index_init_lock);
+        return ret;
 }
+#else /* !SPARSEMEM_EXTREME */
+static inline int sparse_index_init(unsigned long section_nr, int nid)
+{
+        return 0;
+}
+#endif
+
 /* Record a memory area against a node. */
 void memory_present(int nid, unsigned long start, unsigned long end)
 {