mm, show_mem: suppress page counts in non-blockable contexts

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@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e2091b88d24c..f3c7b1f9d1d8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -899,7 +899,8 @@ 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);