sparsemem/bootmem: catch greater than section size allocations

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 -> alloc_bootmem_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 disable the limit check if the size of the allocation in alloc_bootmem_secition exceeds the section size.

Quoted 35 lines · Nishanth Aravamudan

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 -> alloc_bootmem_section calls

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

Quoted 8 lines

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 disable the limit check if the size of the allocation in alloc_bootmem_secition exceeds the section size.

It makes sense to allow the usemaps to spill over to subsequent sections instead of panicking, so FWIW:

Acked-by Johannes Weiner <[email protected]>

That being said, it would be good if check_usemap_section_nr() printed the cross-dependencies between pgdats and sections when the usemaps of a node spilled over to other sections than the ones holding the pgdat.

How about this?

---
From: Johannes Weiner <[email protected]>
Subject: sparsemem/bootmem: catch greater than section size allocations fix

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.

Signed-off-by Johannes Weiner <[email protected]>

---

mm/sparse.c +0 -0

index 61d7cde..9e032dc 100644

---

Furthermore, I wonder if we can remove the sparse-specific stuff from bootmem.c as well, as now even more so than before, calculating the desired area is really none of bootmem's business.

Would something like this be okay?

---
From: Johannes Weiner <[email protected]>
Subject: [patch] mm: remove sparsemem allocation details from the bootmem allocator

alloc_bootmem_section() derives allocation area constraints from the specified sparsemem section. This is a bit specific for a generic memory allocator like bootmem, though, so move it over to sparsemem.

Since __alloc_bootmem_node() already retries failed allocations with relaxed area constraints, the fallback code in sparsemem.c can be removed and the code becomes a bit more compact overall.

Signed-off-by Johannes Weiner <[email protected]>

Quoted 67 lines · Johannes Weiner

Quoted 35 lines · Nishanth Aravamudan

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 -> alloc_bootmem_section calls

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

Quoted 8 lines

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 disable the limit check if the size of the allocation in alloc_bootmem_secition exceeds the section size.

It makes sense to allow the usemaps to spill over to subsequent sections instead of panicking, so FWIW:

Acked-by Johannes Weiner <[email protected]>

That being said, it would be good if check_usemap_section_nr() printed the cross-dependencies between pgdats and sections when the usemaps of a node spilled over to other sections than the ones holding the pgdat.

How about this?

---
From: Johannes Weiner <[email protected]>
Subject: sparsemem/bootmem: catch greater than section size allocations fix

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.

Signed-off-by Johannes Weiner <[email protected]>

---

mm/sparse.c static void __init sparse_early_usemaps_alloc_node(unsigned long**usemap_map, · line 365

Quoted 12 lines

mm/sparse.c +1 -0

index 61d7cde..9e032dc 100644
@@ -359,6 +359,7 @@ static void __init sparse_early_usemaps_alloc_node(unsigned long**usemap_map,
 				continue;
 			usemap_map[pnum] = usemap;
 			usemap += size;
+			check_usemap_section_nr(nodeid, usemap_map[pnum]);
 		}
 		return;
 	}

This makes sense to me -- ok if I fold it into the re-worked patch (based upon Mel's comments)?

Quoted 14 lines

Furthermore, I wonder if we can remove the sparse-specific stuff from bootmem.c as well, as now even more so than before, calculating the desired area is really none of bootmem's business.

Would something like this be okay?

---
From: Johannes Weiner <[email protected]>
Subject: [patch] mm: remove sparsemem allocation details from the bootmem allocator

alloc_bootmem_section() derives allocation area constraints from the specified sparsemem section. This is a bit specific for a generic memory allocator like bootmem, though, so move it over to sparsemem.

Quoted 5 lines

Since __alloc_bootmem_node() already retries failed allocations with relaxed area constraints, the fallback code in sparsemem.c can be removed and the code becomes a bit more compact overall.

Signed-off-by Johannes Weiner <[email protected]>

I've not tested it, but the intention seems sensible. I think it should remain a separate change.

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 -> alloc_bootmem_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 disable the limit check if the size of the allocation in alloc_bootmem_secition exceeds the section size.

Signed-off-by Nishanth Aravamudan <[email protected]>

Cc Dave Hansen <[email protected]>

Cc Anton Blanchard <[email protected]>

Cc Paul Mackerras <[email protected]>

Cc Ben Herrenschmidt <[email protected]>

Cc Robert Jennings <[email protected]>

Cc [email protected]

Cc [email protected]

---
 include/linux/mmzone.h |    2 ++
 mm/bootmem.c           |    5 ++++-
 2 files changed, 6 insertions(+), 1 deletions(-)

include/linux/mmzone.h +2 -0

index 650ba2f..4176834 100644
@@ -967,6 +967,8 @@ static inline unsigned long early_pfn_to_nid(unsigned long pfn)
  * PA_SECTION_SHIFT		physical address to/from section number
  * PFN_SECTION_SHIFT		pfn to/from section number
  */
+#define BYTES_PER_SECTION	(1UL << SECTION_SIZE_BITS)
+
 #define SECTIONS_SHIFT		(MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
 
 #define PA_SECTION_SHIFT	(SECTION_SIZE_BITS)

mm/bootmem.c +0 -0

index 668e94d..5cbbc76 100644

Quoted 76 lines · Nishanth Aravamudan

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 -> alloc_bootmem_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 disable the limit check if the size of the allocation in alloc_bootmem_secition exceeds the section size.

Signed-off-by Nishanth Aravamudan <[email protected]>

Cc Dave Hansen <[email protected]>

Cc Anton Blanchard <[email protected]>

Cc Paul Mackerras <[email protected]>

Cc Ben Herrenschmidt <[email protected]>

Cc Robert Jennings <[email protected]>

Cc [email protected]

Cc [email protected]

---
 include/linux/mmzone.h |    2 ++
 mm/bootmem.c           |    5 ++++-
 2 files changed, 6 insertions(+), 1 deletions(-)

include/linux/mmzone.h +2 -0

index 650ba2f..4176834 100644
@@ -967,6 +967,8 @@ static inline unsigned long early_pfn_to_nid(unsigned long pfn)
  * PA_SECTION_SHIFT		physical address to/from section number
  * PFN_SECTION_SHIFT		pfn to/from section number
  */
+#define BYTES_PER_SECTION	(1UL << SECTION_SIZE_BITS)
+
 #define SECTIONS_SHIFT		(MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
 
 #define PA_SECTION_SHIFT	(SECTION_SIZE_BITS)

mm/bootmem.c +0 -0

index 668e94d..5cbbc76 100644
@@ -770,7 +770,10 @@ void * __init alloc_bootmem_section(unsigned long size,
 

mm/bootmem.c void * __init alloc_bootmem_section(unsigned long size, · line 776

Quoted 7 lines

mm/bootmem.c +4 -1

 	pfn = section_nr_to_pfn(section_nr);
 	goal = pfn << PAGE_SHIFT;
-	limit = section_nr_to_pfn(section_nr + 1) << PAGE_SHIFT;
+	if (size > BYTES_PER_SECTION)
+		limit = 0;
+	else
+		limit = section_nr_to_pfn(section_nr + 1) << PAGE_SHIFT;

As it's ok to spill the allocation over to an adjacent section, why not just make limit==0 unconditionally. That would avoid defining BYTES_PER_SECTION.

Quoted 77 lines · Mel Gorman

Quoted 76 lines · Nishanth Aravamudan

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 -> alloc_bootmem_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 disable the limit check if the size of the allocation in alloc_bootmem_secition exceeds the section size.

Signed-off-by Nishanth Aravamudan <[email protected]>

Cc Dave Hansen <[email protected]>

Cc Anton Blanchard <[email protected]>

Cc Paul Mackerras <[email protected]>

Cc Ben Herrenschmidt <[email protected]>

Cc Robert Jennings <[email protected]>

Cc [email protected]

Cc [email protected]

---
 include/linux/mmzone.h |    2 ++
 mm/bootmem.c           |    5 ++++-
 2 files changed, 6 insertions(+), 1 deletions(-)

include/linux/mmzone.h +2 -0

index 650ba2f..4176834 100644
@@ -967,6 +967,8 @@ static inline unsigned long early_pfn_to_nid(unsigned long pfn)
  * PA_SECTION_SHIFT		physical address to/from section number
  * PFN_SECTION_SHIFT		pfn to/from section number
  */
+#define BYTES_PER_SECTION	(1UL << SECTION_SIZE_BITS)
+
 #define SECTIONS_SHIFT		(MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
 
 #define PA_SECTION_SHIFT	(SECTION_SIZE_BITS)

mm/bootmem.c +0 -0

index 668e94d..5cbbc76 100644
@@ -770,7 +770,10 @@ void * __init alloc_bootmem_section(unsigned long size,
 

Quoted 11 lines

mm/bootmem.c void * __init alloc_bootmem_section(unsigned long size,

Quoted 7 lines

mm/bootmem.c +4 -1

 	pfn = section_nr_to_pfn(section_nr);
 	goal = pfn << PAGE_SHIFT;
-	limit = section_nr_to_pfn(section_nr + 1) << PAGE_SHIFT;
+	if (size > BYTES_PER_SECTION)
+		limit = 0;
+	else
+		limit = section_nr_to_pfn(section_nr + 1) << PAGE_SHIFT;

As it's ok to spill the allocation over to an adjacent section, why not just make limit==0 unconditionally. That would avoid defining BYTES_PER_SECTION.

Something like this?

Andrew, presuming Mel & Johannes give their, ack this should presumably supersede the patch you pulled into -mm.

Thanks,
Nish

-------

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.

Signed-off-by Nishanth Aravamudan <[email protected]>

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.

Quoted 31 lines · On Wed, 29 Feb 2012 10:12:33 -0800 Nishanth Aravamudan…

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).

Quoted 6 lines

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?

mm/bootmem.c renamed from mm/bootmem.c~bootmem-sparsemem-remove-limit-constraint-in-alloc_bootmem_section-fix +1 -1

@@ -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;

Quoted 31 lines · On Wed, 29 Feb 2012 10:12:33 -0800 Nishanth Aravamudan…

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).

Quoted 6 lines

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?

<SNIP>

Signed-off-by Nishanth Aravamudan <[email protected]>