[PATCH 05/18] perf evlist: Do not use hard coded value for a mmap_pages default

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

So far what is in there by default is what we were using: 512KB + the
control page, but the admin may change that, and if it does to a smaller
value, all calls to tooling for non root users start failing, requiring
that the user manually set --mmap_pages/-m.

Use instead what is in /proc/sys/kernel/perf_event_mlock_kb.

Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-2f6mtm8xu3wo5lhkql6jdblh@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/evlist.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 7847f3885081..ac808680e61c 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -893,10 +893,22 @@ out_unmap:
 
 static size_t perf_evlist__mmap_size(unsigned long pages)
 {
-	/* 512 kiB: default amount of unprivileged mlocked memory */
-	if (pages == UINT_MAX)
-		pages = (512 * 1024) / page_size;
-	else if (!is_power_of_2(pages))
+	if (pages == UINT_MAX) {
+		int max;
+
+		if (sysctl__read_int("kernel/perf_event_mlock_kb", &max) < 0) {
+			/*
+			 * Pick a once upon a time good value, i.e. things look
+			 * strange since we can't read a sysctl value, but lets not
+			 * die yet...
+			 */
+			max = 512;
+		} else {
+			max -= (page_size / 1024);
+		}
+
+		pages = (max * 1024) / page_size;
+	} else if (!is_power_of_2(pages))
 		return 0;
 
 	return (pages + 1) * page_size;
-- 
1.9.3

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