[PATCH 3.2 148/149] mm, show_mem: suppress page counts innon-blockable contexts

[Ben Hutchings]

3.2.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: David Rientjes <rientjes@xxxxxxxxxx>

commit 4b59e6c4730978679b414a8da61514a2518da512 upstream.

On large systems with a lot of memory, walking all RAM to determine page
types may take a half second or even more.

In non-blockable contexts, the page allocator will emit a page allocation
failure warning unless __GFP_NOWARN is specified.  In such contexts, irqs
are typically disabled and such a lengthy delay may even result in NMI
watchdog timeouts.

To fix this, suppress the page walk in such contexts when printing the
page allocation failure warning.

Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Cc: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/arm/mm/init.c       | 3 +++
 arch/ia64/mm/contig.c    | 2 ++
 arch/ia64/mm/discontig.c | 2 ++
 arch/parisc/mm/init.c    | 2 ++
 arch/unicore32/mm/init.c | 3 +++
 include/linux/mm.h       | 3 ++-
 lib/show_mem.c           | 3 +++
 mm/page_alloc.c          | 7 +++++++
 8 files changed, 24 insertions(+), 1 deletion(-)

--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -98,6 +98,9 @@ void show_mem(unsigned int filter)
 	printk("Mem-info:\n");
 	show_free_areas(filter);
 
+	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
+		return;
+
 	for_each_bank (i, mi) {
 		struct membank *bank = &mi->bank[i];
 		unsigned int pfn1, pfn2;
--- a/arch/ia64/mm/contig.c
+++ b/arch/ia64/mm/contig.c
@@ -46,6 +46,8 @@ void show_mem(unsigned int filter)
 	printk(KERN_INFO "Mem-info:\n");
 	show_free_areas(filter);
 	printk(KERN_INFO "Node memory in pages:\n");
+	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
+		return;
 	for_each_online_pgdat(pgdat) {
 		unsigned long present;
 		unsigned long flags;
--- a/arch/ia64/mm/discontig.c
+++ b/arch/ia64/mm/discontig.c
@@ -623,6 +623,8 @@ void show_mem(unsigned int filter)
 
 	printk(KERN_INFO "Mem-info:\n");
 	show_free_areas(filter);
+	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
+		return;
 	printk(KERN_INFO "Node memory in pages:\n");
 	for_each_online_pgdat(pgdat) {
 		unsigned long present;
--- a/arch/parisc/mm/init.c
+++ b/arch/parisc/mm/init.c
@@ -685,6 +685,8 @@ void show_mem(unsigned int filter)
 
 	printk(KERN_INFO "Mem-info:\n");
 	show_free_areas(filter);
+	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
+		return;
 #ifndef CONFIG_DISCONTIGMEM
 	i = max_mapnr;
 	while (i-- > 0) {
--- a/arch/unicore32/mm/init.c
+++ b/arch/unicore32/mm/init.c
@@ -65,6 +65,9 @@ void show_mem(unsigned int filter)
 	printk(KERN_DEFAULT "Mem-info:\n");
 	show_free_areas(filter);
 
+	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
+		return;
+
 	for_each_bank(i, mi) {
 		struct membank *bank = &mi->bank[i];
 		unsigned int pfn1, pfn2;
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -865,7 +865,8 @@ extern void pagefault_out_of_memory(void
  * Flags passed to show_mem() and show_free_areas() to suppress output in
  * various contexts.
  */
-#define SHOW_MEM_FILTER_NODES	(0x0001u)	/* filter disallowed nodes */
+#define SHOW_MEM_FILTER_NODES		(0x0001u)	/* disallowed nodes */
+#define SHOW_MEM_FILTER_PAGE_COUNT	(0x0002u)	/* page type count */
 
 extern void show_free_areas(unsigned int flags);
 extern bool skip_free_areas_node(unsigned int flags, int nid);
--- a/lib/show_mem.c
+++ b/lib/show_mem.c
@@ -18,6 +18,9 @@ void show_mem(unsigned int filter)
 	printk("Mem-Info:\n");
 	show_free_areas(filter);
 
+	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
+		return;
+
 	for_each_online_pgdat(pgdat) {
 		unsigned long i, flags;
 
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1760,6 +1760,13 @@ void warn_alloc_failed(gfp_t gfp_mask, i
 		return;
 
 	/*
+	 * Walking all memory to count page types is very expensive and should
+	 * be inhibited in non-blockable contexts.
+	 */
+	if (!(gfp_mask & __GFP_WAIT))
+		filter |= SHOW_MEM_FILTER_PAGE_COUNT;
+
+	/*
 	 * This documents exceptions given to allocations in certain
 	 * contexts that are allowed to allocate outside current's set
 	 * of allowed nodes.

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