[patch 1/2] mm: sparse: fix section usemap placement calculation

[patch 1/2] mm: sparse: fix section usemap placement calculation

[Johannes Weiner]

From: Yinghai Lu <yinghai@kernel.org>

238305b "mm: remove sparsemem allocation details from the bootmem
allocator" introduced a bug in the allocation goal calculation that
put section usemaps not in the same section as the node descriptors,
creating unnecessary hotplug dependencies between them:

[    0.000000] node 0 must be removed before remove section 16399
[    0.000000] node 1 must be removed before remove section 16399
[    0.000000] node 2 must be removed before remove section 16399
[    0.000000] node 3 must be removed before remove section 16399
[    0.000000] node 4 must be removed before remove section 16399
[    0.000000] node 5 must be removed before remove section 16399
[    0.000000] node 6 must be removed before remove section 16399

The reason is that it applies PAGE_SECTION_MASK to the physical
address of the node descriptor when finding a suitable place to put
the usemap, when this mask is actually intended to be used with PFNs.
Because the PFN mask is wider, the target address will point beyond
the wanted section holding the node descriptor and the node must be
offlined before the section holding the usemap can go.

Fix this by extending the mask to address width before use.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/sparse.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 6a4bf91..e861397 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -287,7 +287,7 @@ sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
 	 * from the same section as the pgdat where possible to avoid
 	 * this problem.
 	 */
-	goal = __pa(pgdat) & PAGE_SECTION_MASK;
+	goal = __pa(pgdat) & (PAGE_SECTION_MASK << PAGE_SHIFT);
 	host_pgdat = NODE_DATA(early_pfn_to_nid(goal >> PAGE_SHIFT));
 	return __alloc_bootmem_node_nopanic(host_pgdat, size,
 					    SMP_CACHE_BYTES, goal);
-- 
1.7.7.6

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[patch 2/2] mm: sparse: fix usemap allocation above node descriptor section

[Johannes Weiner]

From: Yinghai Lu <yinghai@kernel.org>

After f5bf18f "bootmem/sparsemem: remove limit constraint in
alloc_bootmem_section", usemap allocations may easily be placed
outside the optimal section that holds the node descriptor, even if
there is space available in that section.  This results in unnecessary
hotplug dependencies that need to have the node unplugged before the
section holding the usemap.

The reason is that the bootmem allocator doesn't guarantee a linear
search starting from the passed allocation goal but may start out at a
much higher address absent an upper limit.

Fix this by trying the allocation with the limit at the section end,
then retry without if that fails.  This keeps the fix from f5bf18f of
not panicking if the allocation does not fit in the section, but still
makes sure to try to stay within the section at first.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: stable@kernel.org [3.3, 3.4]
---
 include/linux/bootmem.h |    5 +++++
 mm/bootmem.c            |    2 +-
 mm/nobootmem.c          |    2 +-
 mm/sparse.c             |   18 +++++++++++++-----
 4 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h
index 324fe08..6d6795d 100644
--- a/include/linux/bootmem.h
+++ b/include/linux/bootmem.h
@@ -91,6 +91,11 @@ extern void *__alloc_bootmem_node_nopanic(pg_data_t *pgdat,
 				  unsigned long size,
 				  unsigned long align,
 				  unsigned long goal);
+void *___alloc_bootmem_node_nopanic(pg_data_t *pgdat,
+				  unsigned long size,
+				  unsigned long align,
+				  unsigned long goal,
+				  unsigned long limit);
 extern void *__alloc_bootmem_low(unsigned long size,
 				 unsigned long align,
 				 unsigned long goal);
diff --git a/mm/bootmem.c b/mm/bootmem.c
index ec4fcb7..7309663 100644
--- a/mm/bootmem.c
+++ b/mm/bootmem.c
@@ -698,7 +698,7 @@ void * __init __alloc_bootmem(unsigned long size, unsigned long align,
 	return ___alloc_bootmem(size, align, goal, limit);
 }
 
-static void * __init ___alloc_bootmem_node_nopanic(pg_data_t *pgdat,
+void * __init ___alloc_bootmem_node_nopanic(pg_data_t *pgdat,
 				unsigned long size, unsigned long align,
 				unsigned long goal, unsigned long limit)
 {
diff --git a/mm/nobootmem.c b/mm/nobootmem.c
index 6773ba5..4055730 100644
--- a/mm/nobootmem.c
+++ b/mm/nobootmem.c
@@ -282,7 +282,7 @@ void * __init __alloc_bootmem(unsigned long size, unsigned long align,
 	return ___alloc_bootmem(size, align, goal, limit);
 }
 
-static void * __init ___alloc_bootmem_node_nopanic(pg_data_t *pgdat,
+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 e861397..c7bb952 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -275,8 +275,9 @@ static unsigned long * __init
 sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
 					 unsigned long size)
 {
-	pg_data_t *host_pgdat;
-	unsigned long goal;
+	unsigned long goal, limit;
+	unsigned long *p;
+	int nid;
 	/*
 	 * A page may contain usemaps for other sections preventing the
 	 * page being freed and making a section unremovable while
@@ -288,9 +289,16 @@ sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
 	 * this problem.
 	 */
 	goal = __pa(pgdat) & (PAGE_SECTION_MASK << PAGE_SHIFT);
-	host_pgdat = NODE_DATA(early_pfn_to_nid(goal >> PAGE_SHIFT));
-	return __alloc_bootmem_node_nopanic(host_pgdat, size,
-					    SMP_CACHE_BYTES, goal);
+	limit = goal + (1UL << PA_SECTION_SHIFT);
+	nid = early_pfn_to_nid(goal >> PAGE_SHIFT);
+again:
+	p = ___alloc_bootmem_node_nopanic(NODE_DATA(nid), size,
+					  SMP_CACHE_BYTES, goal, limit);
+	if (!p && limit) {
+		limit = 0;
+		goto again;
+	}
+	return p;
 }
 
 static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
-- 
1.7.7.6

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