linux-kernel - [PATCH v2 11/13] libperf: Lazily allocate mmap event copy

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Message-Id: <20231012062359.1616786-12-irogers@google.com>
Date:   Wed, 11 Oct 2023 23:23:57 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Nick Terrell <terrelln@...com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Song Liu <song@...nel.org>,
        Sandipan Das <sandipan.das@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        James Clark <james.clark@....com>,
        Liam Howlett <liam.howlett@...cle.com>,
        Miguel Ojeda <ojeda@...nel.org>, Leo Yan <leo.yan@...aro.org>,
        German Gomez <german.gomez@....com>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Artem Savkov <asavkov@...hat.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH v2 11/13] libperf: Lazily allocate mmap event copy

The event copy in the mmap is used to have storage to a read
event. Not all users of mmaps read the events, such as perf record, so
switch the allocation to being on first read rather than being
embedded within the perf_mmap.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/lib/perf/include/internal/mmap.h | 2 +-
 tools/lib/perf/mmap.c                  | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/lib/perf/include/internal/mmap.h b/tools/lib/perf/include/internal/mmap.h
index 5a062af8e9d8..b11aaf5ed645 100644
--- a/tools/lib/perf/include/internal/mmap.h
+++ b/tools/lib/perf/include/internal/mmap.h
@@ -33,7 +33,7 @@ struct perf_mmap {
 	bool			 overwrite;
 	u64			 flush;
 	libperf_unmap_cb_t	 unmap_cb;
-	char			 event_copy[PERF_SAMPLE_MAX_SIZE] __aligned(8);
+	void			*event_copy;
 	struct perf_mmap	*next;
 };
 
diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
index 2184814b37dd..91ae46aac378 100644
--- a/tools/lib/perf/mmap.c
+++ b/tools/lib/perf/mmap.c
@@ -51,6 +51,8 @@ int perf_mmap__mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
 
 void perf_mmap__munmap(struct perf_mmap *map)
 {
+	free(map->event_copy);
+	map->event_copy = NULL;
 	if (map && map->base != NULL) {
 		munmap(map->base, perf_mmap__mmap_len(map));
 		map->base = NULL;
@@ -226,6 +228,13 @@ static union perf_event *perf_mmap__read(struct perf_mmap *map,
 			unsigned int len = min(sizeof(*event), size), cpy;
 			void *dst = map->event_copy;
 
+			if (!dst) {
+				dst = malloc(PERF_SAMPLE_MAX_SIZE);
+				if (!dst)
+					return NULL;
+				map->event_copy = dst;
+			}
+
 			do {
 				cpy = min(map->mask + 1 - (offset & map->mask), len);
 				memcpy(dst, &data[offset & map->mask], cpy);
-- 
2.42.0.609.gbb76f46606-goog