[PATCH v1 6/7] perf session: Periodically shrink symbols and DSOs during event processing

[Ian Rogers]

Add periodic calls to perf_session__shrink() so that both live profiling
and trace-processing commands reclaim unused symbol and DSO memory:

- In perf_session__deliver_event(), trigger perf_session__shrink()
  every 16,384 events, or after at least 512 events when at least
  65,536 new symbols have been inserted across DSOs (tracked via
  symbols__inserted_cnt()). This bounds memory usage for session-based
  commands such as 'perf script' and 'perf report' even on short traces
  that load many large binaries, while giving hot symbols in newly
  loaded DSOs a window to be marked SYMBOL_FLAG_ACCESSED.
- In perf_top__resort_hists(), call perf_session__shrink() on each
  display refresh cycle so 'perf top' periodically ages out unused
  symbols and DSOs.

Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/builtin-top.c  |  2 ++
 tools/perf/util/session.c | 16 ++++++++++++++++
 tools/perf/util/session.h | 10 ++++++++++
 tools/perf/util/symbol.c  | 15 +++++++++++++++
 tools/perf/util/symbol.h  |  1 +
 5 files changed, 44 insertions(+)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index dd1e475bb4dd..c96530f33fe4 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -320,6 +320,8 @@ static void perf_top__resort_hists(struct perf_top *t)
 	evlist__for_each_entry(evlist, pos) {
 		evsel__output_resort(pos, NULL);
 	}
+
+	perf_session__shrink(t->session);
 }
 
 static void perf_top__print_sym_table(struct perf_top *top)
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 555d940a866a..74a564c6589b 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -164,6 +164,7 @@ struct perf_session *__perf_session__new(struct perf_data *data,
 	session->tool   = tool;
 	session->decomp_data.zstd_decomp = &session->zstd_data;
 	session->active_decomp = &session->decomp_data;
+	session->last_symbols_inserted = symbols__inserted_cnt();
 	INIT_LIST_HEAD(&session->auxtrace_index);
 	perf_env__init(&session->header.env);
 	if (machines__init(&session->machines, session))
@@ -2351,6 +2352,19 @@ static int perf_session__deliver_event(struct perf_session *session,
 
 	if (dump_trace && sample.aux_sample.size)
 		auxtrace__dump_auxtrace_sample(session, &sample);
+
+	/*
+	 * Periodically reclaim unreferenced symbols, DSO caches, and cold DSOs
+	 * during event processing (e.g., perf script, perf report). Trigger
+	 * either every 16,384 events, or after at least 512 events when more
+	 * than 65,536 symbols have been newly loaded across DSOs.
+	 */
+	session->events_since_shrink++;
+	if (session->events_since_shrink >= 16384 ||
+	    (session->events_since_shrink >= 512 &&
+	     symbols__inserted_cnt() - session->last_symbols_inserted >= 65536)) {
+		perf_session__shrink(session);
+	}
 out:
 	perf_sample__exit(&sample);
 	return ret;
@@ -3945,6 +3959,8 @@ size_t perf_session__shrink(struct perf_session *session)
 	if (!session)
 		return 0;
 
+	session->events_since_shrink = 0;
+	session->last_symbols_inserted = symbols__inserted_cnt();
 	return machines__shrink(&session->machines);
 }
 
diff --git a/tools/perf/util/session.h b/tools/perf/util/session.h
index 4b223c2cee7f..030d5e931160 100644
--- a/tools/perf/util/session.h
+++ b/tools/perf/util/session.h
@@ -95,6 +95,16 @@ struct perf_session {
 	struct decomp_data	decomp_data;
 	/** @active_decomp: Currently active decompression context. */
 	struct decomp_data	*active_decomp;
+	/**
+	 * @events_since_shrink: Number of events delivered via
+	 * perf_session__deliver_event() since the last perf_session__shrink().
+	 */
+	u64			events_since_shrink;
+	/**
+	 * @last_symbols_inserted: Snapshot of symbols__inserted_cnt() taken at
+	 * the last perf_session__shrink() pass.
+	 */
+	unsigned long		last_symbols_inserted;
 };
 
 struct decomp {
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 33cfd86156d2..57894c3dc5b5 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -623,6 +623,20 @@ static void symbol__set_idle(struct symbol *sym, bool idle)
 	} while (!atomic_compare_exchange_weak(&RC_CHK_ACCESS(sym)->flags, &old_flags, new_flags));
 }
 
+static atomic_ulong symbols_inserted_cnt;
+
+/**
+ * symbols__inserted_cnt - Return cumulative count of symbols inserted.
+ *
+ * Monotonically increasing counter incremented each time a symbol is inserted
+ * into a struct symbols collection. Used by perf_session__deliver_event() to
+ * detect burst symbol loading across large DSOs and trigger periodic shrinking.
+ */
+unsigned long symbols__inserted_cnt(void)
+{
+	return atomic_load_explicit(&symbols_inserted_cnt, memory_order_relaxed);
+}
+
 int __symbols__insert(struct symbols *symbols, struct symbol *sym)
 {
 	if (symbols->cnt == symbols->allocated) {
@@ -644,6 +658,7 @@ int __symbols__insert(struct symbols *symbols, struct symbol *sym)
 
 	symbols->symbols[symbols->cnt++] = sym;
 	symbols->sorted_by_name = false;
+	atomic_fetch_add_explicit(&symbols_inserted_cnt, 1, memory_order_relaxed);
 	return 0;
 }
 
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index a76613c43ba9..783d9735aa3f 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -162,6 +162,7 @@ void symbols__exit(struct symbols *symbols);
 void symbols__delete(struct symbols *symbols);
 void symbols__sort_read_lock(struct symbols *symbols) SHARED_LOCK_FUNCTION(symbols->lock);
 size_t symbols__shrink(struct symbols *symbols);
+unsigned long symbols__inserted_cnt(void);
 
 static inline refcount_t *symbol__refcnt(struct symbol *sym)
 {
-- 
2.56.0.rc1.315.gc6ed9934b7-goog