[PATCH] mm: simplify nodemask printing

[Michal Hocko]

alloc_warn and dump_header have to explicitly handle NULL nodemask which
forces both paths to use pr_cont. We can do better. printk already
handles NULL pointers properly so all what we need is to teach
nodemask_pr_args to handle NULL nodemask carefully. This allows
simplification of both alloc_warn and dump_header and get rid of pr_cont
altogether.

This patch has been motivated by patch from Joe Perches
http://lkml.kernel.org/r/b31236dfe3fc924054fd7842bde678e71d193638.1509991345.git.joe@xxxxxxxxxxx

Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 include/linux/nodemask.h |  2 +-
 mm/oom_kill.c            | 12 ++++--------
 mm/page_alloc.c          | 12 +++---------
 3 files changed, 8 insertions(+), 18 deletions(-)

diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
index cf0b91c3ec12..5d3cc67207ed 100644
--- a/include/linux/nodemask.h
+++ b/include/linux/nodemask.h
@@ -103,7 +103,7 @@ extern nodemask_t _unused_nodemask_arg_;
  *
  * Can be used to provide arguments for '%*pb[l]' when printing a nodemask.
  */
-#define nodemask_pr_args(maskp)		MAX_NUMNODES, (maskp)->bits
+#define nodemask_pr_args(maskp)	(maskp) ? MAX_NUMNODES : 0, (maskp) ? (maskp)->bits : NULL
 
 /*
  * The inline keyword gives the compiler room to decide to inline, or
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 8dd0e088189b..606213a81ceb 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -426,14 +426,10 @@ static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
 
 static void dump_header(struct oom_control *oc, struct task_struct *p)
 {
-	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), nodemask=",
-		current->comm, oc->gfp_mask, &oc->gfp_mask);
-	if (oc->nodemask)
-		pr_cont("%*pbl", nodemask_pr_args(oc->nodemask));
-	else
-		pr_cont("(null)");
-	pr_cont(",  order=%d, oom_score_adj=%hd\n",
-		oc->order, current->signal->oom_score_adj);
+	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), nodemask=%*pbl, order=%d, oom_score_adj=%hd\n",
+		current->comm, oc->gfp_mask, &oc->gfp_mask,
+		nodemask_pr_args(oc->nodemask), oc->order,
+			current->signal->oom_score_adj);
 	if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
 		pr_warn("COMPACTION is disabled!!!\n");
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d755434aee94..457e43ed4c10 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3281,20 +3281,14 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
 	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs))
 		return;
 
-	pr_warn("%s: ", current->comm);
-
 	va_start(args, fmt);
 	vaf.fmt = fmt;
 	vaf.va = &args;
-	pr_cont("%pV", &vaf);
+	pr_warn("%s: %pV, mode:%#x(%pGg), nodemask=%*pbl\n",
+			current->comm, &vaf, gfp_mask, &gfp_mask,
+			nodemask_pr_args(nodemask));
 	va_end(args);
 
-	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();
-- 
2.14.2

-- 
Michal Hocko
SUSE Labs