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, 7 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7ff1536f01b8..da7a2fe7332e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2003,6 +2003,13 @@ void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...)
                 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.