bootmem/sparsemem: remove limit constraint in alloc_bootmem_section
Nishanth Aravamudan [Wed, 21 Mar 2012 23:34:07 +0000 (16:34 -0700)]
While testing AMS (Active Memory Sharing) / CMO (Cooperative Memory
Overcommit) on powerpc, we tripped the following:

  kernel BUG at mm/bootmem.c:483!
  cpu 0x0: Vector: 700 (Program Check) at [c000000000c03940]
      pc: c000000000a62bd8: .alloc_bootmem_core+0x90/0x39c
      lr: c000000000a64bcc: .sparse_early_usemaps_alloc_node+0x84/0x29c
      sp: c000000000c03bc0
     msr: 8000000000021032
    current = 0xc000000000b0cce0
    paca    = 0xc000000001d80000
      pid   = 0, comm = swapper
  kernel BUG at mm/bootmem.c:483!
  enter ? for help
  [c000000000c03c80] c000000000a64bcc
  .sparse_early_usemaps_alloc_node+0x84/0x29c
  [c000000000c03d50] c000000000a64f10 .sparse_init+0x12c/0x28c
  [c000000000c03e20] c000000000a474f4 .setup_arch+0x20c/0x294
  [c000000000c03ee0] c000000000a4079c .start_kernel+0xb4/0x460
  [c000000000c03f90] c000000000009670 .start_here_common+0x1c/0x2c

This is

        BUG_ON(limit && goal + size > limit);

and after some debugging, it seems that

goal = 0x7ffff000000
limit = 0x80000000000

and sparse_early_usemaps_alloc_node ->
sparse_early_usemaps_alloc_pgdat_section calls

return alloc_bootmem_section(usemap_size() * count, section_nr);

This is on a system with 8TB available via the AMS pool, and as a quirk
of AMS in firmware, all of that memory shows up in node 0.  So, we end
up with an allocation that will fail the goal/limit constraints.

In theory, we could "fall-back" to alloc_bootmem_node() in
sparse_early_usemaps_alloc_node(), but since we actually have HOTREMOVE
defined, we'll BUG_ON() instead.  A simple solution appears to be to
unconditionally remove the limit condition in alloc_bootmem_section,
meaning allocations are allowed to cross section boundaries (necessary
for systems of this size).

Johannes Weiner pointed out that if alloc_bootmem_section() no longer
guarantees section-locality, we need check_usemap_section_nr() to print
possible cross-dependencies between node descriptors and the usemaps
allocated through it.  That makes the two loops in
sparse_early_usemaps_alloc_node() identical, so re-factor the code a
bit.

[akpm@linux-foundation.org: code simplification]
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Anton Blanchard <anton@au1.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ben Herrenschmidt <benh@kernel.crashing.org>
Cc: Robert Jennings <rcj@linux.vnet.ibm.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: <stable@vger.kernel.org> [3.3.1]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/bootmem.c
mm/sparse.c

index 668e94d..0131170 100644 (file)
@@ -766,14 +766,13 @@ void * __init alloc_bootmem_section(unsigned long size,
                                    unsigned long section_nr)
 {
        bootmem_data_t *bdata;
-       unsigned long pfn, goal, limit;
+       unsigned long pfn, goal;
 
        pfn = section_nr_to_pfn(section_nr);
        goal = pfn << PAGE_SHIFT;
-       limit = section_nr_to_pfn(section_nr + 1) << PAGE_SHIFT;
        bdata = &bootmem_node_data[early_pfn_to_nid(pfn)];
 
-       return alloc_bootmem_core(bdata, size, SMP_CACHE_BYTES, goal, limit);
+       return alloc_bootmem_core(bdata, size, SMP_CACHE_BYTES, goal, 0);
 }
 #endif
 
index 61d7cde..a8bc7d3 100644 (file)
@@ -353,29 +353,21 @@ static void __init sparse_early_usemaps_alloc_node(unsigned long**usemap_map,
 
        usemap = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nodeid),
                                                                 usemap_count);
-       if (usemap) {
-               for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
-                       if (!present_section_nr(pnum))
-                               continue;
-                       usemap_map[pnum] = usemap;
-                       usemap += size;
+       if (!usemap) {
+               usemap = alloc_bootmem_node(NODE_DATA(nodeid), size * usemap_count);
+               if (!usemap) {
+                       printk(KERN_WARNING "%s: allocation failed\n", __func__);
+                       return;
                }
-               return;
        }
 
-       usemap = alloc_bootmem_node(NODE_DATA(nodeid), size * usemap_count);
-       if (usemap) {
-               for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
-                       if (!present_section_nr(pnum))
-                               continue;
-                       usemap_map[pnum] = usemap;
-                       usemap += size;
-                       check_usemap_section_nr(nodeid, usemap_map[pnum]);
-               }
-               return;
+       for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
+               if (!present_section_nr(pnum))
+                       continue;
+               usemap_map[pnum] = usemap;
+               usemap += size;
+               check_usemap_section_nr(nodeid, usemap_map[pnum]);
        }
-
-       printk(KERN_WARNING "%s: allocation failed\n", __func__);
 }
 
 #ifndef CONFIG_SPARSEMEM_VMEMMAP