linux-kernel - [patch -mm] mm, page_alloc: warn_alloc nodemask is NULL when cpusets are disabled

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Date:   Wed, 18 Jan 2017 13:51:14 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>
cc:     Johannes Weiner <hannes@...xchg.org>, Mel Gorman <mgorman@...e.de>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: [patch -mm] mm, page_alloc: warn_alloc nodemask is NULL when cpusets
 are disabled

The patch "mm, page_alloc: warn_alloc print nodemask" implicitly sets the 
allocation nodemask to cpuset_current_mems_allowed when there is no 
effective mempolicy.  cpuset_current_mems_allowed is only effective when 
cpusets are enabled, which is also printed by warn_alloc(), so setting 
the nodemask to cpuset_current_mems_allowed is redundant and prevents 
debugging issues where ac->nodemask is not set properly in the page 
allocator.

This provides better debugging output since 
cpuset_print_current_mems_allowed() is already provided.

Signed-off-by: David Rientjes <rientjes@...gle.com>
---
 mm/page_alloc.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3037,7 +3037,6 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
 	va_list args;
 	static DEFINE_RATELIMIT_STATE(nopage_rs, DEFAULT_RATELIMIT_INTERVAL,
 				      DEFAULT_RATELIMIT_BURST);
-	nodemask_t *nm = (nodemask) ? nodemask : &cpuset_current_mems_allowed;
 
 	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs) ||
 	    debug_guardpage_minorder() > 0)
@@ -3051,11 +3050,16 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
 	pr_cont("%pV", &vaf);
 	va_end(args);
 
-	pr_cont(", mode:%#x(%pGg), nodemask=%*pbl\n", gfp_mask, &gfp_mask, nodemask_pr_args(nm));
+	pr_cont(", mode:%#x(%pGg), nodemask=", gfp_mask, &gfp_mask);
+	if (nodemask)
+		pr_cont("%*pbl\n", nodemask_pr_args(nodemask));
+	else
+		pr_cont("(null)\n");
+
 	cpuset_print_current_mems_allowed();
 
 	dump_stack();
-	warn_alloc_show_mem(gfp_mask, nm);
+	warn_alloc_show_mem(gfp_mask, nodemask);
 }
 
 static inline struct page *