On Fri, Feb 24, 2012 at 11:33:58AM -0800, Nishanth Aravamudan wrote:
> 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.
It makes sense to allow the usemaps to spill over to subsequent
sections instead of panicking, so FWIW:
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
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 <hannes@xxxxxxxxxxx>
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 <hannes@xxxxxxxxxxx>
---
diff --git a/mm/sparse.c b/mm/sparse.c
index 61d7cde..9e032dc 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -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;
}
---
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 <hannes@xxxxxxxxxxx>
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 <hannes@xxxxxxxxxxx>
---
include/linux/bootmem.h | 3 ---
mm/bootmem.c | 26 --------------------------
mm/sparse.c | 29 +++++++++--------------------
3 files changed, 9 insertions(+), 49 deletions(-)
diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h
index ab344a5..001c248 100644
--- a/include/linux/bootmem.h
+++ b/include/linux/bootmem.h
@@ -135,9 +135,6 @@ extern void *__alloc_bootmem_low_node(pg_data_t *pgdat,
extern int reserve_bootmem_generic(unsigned long addr, unsigned long size,
int flags);
-extern void *alloc_bootmem_section(unsigned long size,
- unsigned long section_nr);
-
#ifdef CONFIG_HAVE_ARCH_ALLOC_REMAP
extern void *alloc_remap(int nid, unsigned long size);
#else
diff --git a/mm/bootmem.c b/mm/bootmem.c
index 7bc0557..d34026c 100644
--- a/mm/bootmem.c
+++ b/mm/bootmem.c
@@ -756,32 +756,6 @@ void * __init __alloc_bootmem_node_high(pg_data_t *pgdat, unsigned long size,
}
-#ifdef CONFIG_SPARSEMEM
-/**
- * alloc_bootmem_section - allocate boot memory from a specific section
- * @size: size of the request in bytes
- * @section_nr: sparse map section to allocate from
- *
- * Return NULL on failure.
- */
-void * __init alloc_bootmem_section(unsigned long size,
- unsigned long section_nr)
-{
- bootmem_data_t *bdata;
- unsigned long pfn, goal, limit;
-
- pfn = section_nr_to_pfn(section_nr);
- goal = pfn << PAGE_SHIFT;
- if (size > BYTES_PER_SECTION)
- limit = 0;
- else
- 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);
-}
-#endif
-
void * __init __alloc_bootmem_node_nopanic(pg_data_t *pgdat, unsigned long size,
unsigned long align, unsigned long goal)
{
diff --git a/mm/sparse.c b/mm/sparse.c
index 9e032dc..ac0d5a3 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -273,10 +273,10 @@ static unsigned long *__kmalloc_section_usemap(void)
#ifdef CONFIG_MEMORY_HOTREMOVE
static unsigned long * __init
sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
- unsigned long count)
+ unsigned long size)
{
- unsigned long section_nr;
-
+ pg_data_t *host_pgdat;
+ unsigned long goal;
/*
* A page may contain usemaps for other sections preventing the
* page being freed and making a section unremovable while
@@ -287,8 +287,9 @@ sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
* from the same section as the pgdat where possible to avoid
* this problem.
*/
- section_nr = pfn_to_section_nr(__pa(pgdat) >> PAGE_SHIFT);
- return alloc_bootmem_section(usemap_size() * count, section_nr);
+ goal = __pa(pgdat) & PAGE_SECTION_MASK;
+ host_pgdat = NODE_DATA(early_pfn_to_nid(goal));
+ return __alloc_bootmem_node(host_pgdat, size, SMP_CACHE_BYTES, goal);
}
static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
@@ -332,9 +333,9 @@ static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
#else
static unsigned long * __init
sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
- unsigned long count)
+ unsigned long size)
{
- return NULL;
+ return alloc_bootmem_node(pgdat, size);
}
static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
@@ -352,19 +353,7 @@ static void __init sparse_early_usemaps_alloc_node(unsigned long**usemap_map,
int size = usemap_size();
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;
- check_usemap_section_nr(nodeid, usemap_map[pnum]);
- }
- return;
- }
-
- usemap = alloc_bootmem_node(NODE_DATA(nodeid), size * usemap_count);
+ size * usemap_count);
if (usemap) {
for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
if (!present_section_nr(pnum))
--
1.7.7.6
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