On Wed, 29 Feb 2012 10:12:33 -0800
Nishanth Aravamudan <nacc@xxxxxxxxxxxxxxxxxx> wrote:
> While testing AMS (Active Memory Sharing) / CMO (Cooperative Memory
> Overcommit) on powerpc, we tripped the following:
>
> kernel BUG at mm/bootmem.c:483!
>
> ...
>
> 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.
The patch is a bit scary now, so I think we should merge it into
3.4-rc1 and then backport it into 3.3.1 if nothing blows up.
Do you think it should be backported into 3.3.x? Earlier kernels?
Also, this?
--- a/mm/bootmem.c~bootmem-sparsemem-remove-limit-constraint-in-alloc_bootmem_section-fix
+++ a/mm/bootmem.c
@@ -766,14 +766,13 @@ void * __init alloc_bootmem_section(unsi
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 = 0;
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
_
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