Add a simple utility to detect profiling bias.

Makefile.in

@@ -294,7 +294,8 @@ CPP_SRCS :=
 TESTS_INTEGRATION_CPP :=
 endif
 TESTS_ANALYZE := $(srcroot)test/analyze/rand.c \
-	$(srcroot)test/analyze/sizes.c
+	$(srcroot)test/analyze/sizes.c \
+	$(srcroot)test/analyze/prof_bias.c
 TESTS_STRESS := $(srcroot)test/stress/microbench.c \
 	$(srcroot)test/stress/fill_flush.c \
 	$(srcroot)test/stress/large_microbench.c \

include/jemalloc/internal/prof_externs.h

@@ -43,6 +43,13 @@ extern size_t lg_prof_sample;
 
 extern bool prof_booted;
 
+/*
+ * A hook to mock out backtrace functionality.  This can be handy, since it's
+ * otherwise difficult to guarantee that two allocations are reported as coming
+ * from the exact same stack trace in the presence of an optimizing compiler.
+ */
+extern void (* JET_MUTABLE prof_backtrace_hook)(prof_bt_t *bt);
+
 /* Functions only accessed in prof_inlines.h */
 prof_tdata_t *prof_tdata_init(tsd_t *tsd);
 prof_tdata_t *prof_tdata_reinit(tsd_t *tsd, prof_tdata_t *tdata);

src/prof_sys.c

@@ -27,6 +27,8 @@
 
 malloc_mutex_t prof_dump_filename_mtx;
 
+bool prof_do_mock = false;
+
 static uint64_t prof_dump_seq;
 static uint64_t prof_dump_iseq;
 static uint64_t prof_dump_mseq;
@@ -267,11 +269,14 @@ prof_backtrace_impl(prof_bt_t *bt) {
 }
 #endif
 
+
+void (* JET_MUTABLE prof_backtrace_hook)(prof_bt_t *bt) = &prof_backtrace_impl;
+
 void
 prof_backtrace(tsd_t *tsd, prof_bt_t *bt) {
 	cassert(config_prof);
 	pre_reentrancy(tsd, NULL);
-	prof_backtrace_impl(bt);
+	prof_backtrace_hook(bt);
 	post_reentrancy(tsd);
 }
 

test/analyze/prof_bias.c

@@ -0,0 +1,60 @@
+#include "test/jemalloc_test.h"
+
+/*
+ * This is a helper utility, only meant to be run manually (and, for example,
+ * doesn't check for failures, try to skip execution in non-prof modes, etc.).
+ * It runs, allocates objects of two different sizes from the same stack trace,
+ * and exits.
+ *
+ * The idea is that some human operator will run it like:
+ *     MALLOC_CONF="prof:true,prof_final:true" test/analyze/prof_bias
+ * and manually inspect the results.
+ *
+ * The results should be:
+ * jeprof --text test/analyze/prof_bias --inuse_space jeprof.<pid>.0.f.heap:
+ * 	around 1024 MB
+ * jeprof --text test/analyze/prof_bias --inuse_objects jeprof.<pid>.0.f.heap:
+ * 	around 33554448 = 16 + 32 * 1024 * 1024
+ *
+ * And, if prof_accum is on:
+ * jeprof --text test/analyze/prof_bias --alloc_space jeprof.<pid>.0.f.heap:
+ *     around 2048 MB
+ * jeprof --text test/analyze/prof_bias --alloc_objects jeprof.<pid>.0.f.heap:
+ * 	around 67108896 = 2 * (16 + 32 * 1024 * 1024)
+ */
+
+static void
+mock_backtrace(prof_bt_t *bt) {
+	bt->len = 4;
+	bt->vec[0] = (void *)0x111;
+	bt->vec[1] = (void *)0x222;
+	bt->vec[2] = (void *)0x333;
+	bt->vec[3] = (void *)0x444;
+}
+
+static void
+do_allocs(size_t sz, size_t cnt, bool do_frees) {
+	for (size_t i = 0; i < cnt; i++) {
+		void *ptr = mallocx(sz, 0);
+		assert_ptr_not_null(ptr, "Unexpected mallocx failure");
+		if (do_frees) {
+			dallocx(ptr, 0);
+		}
+	}
+}
+
+int
+main(void) {
+	size_t lg_prof_sample = 19;
+	int err = mallctl("prof.reset", NULL, NULL, (void *)&lg_prof_sample,
+	    sizeof(lg_prof_sample));
+	assert(err == 0);
+
+	prof_backtrace_hook = &mock_backtrace;
+	do_allocs(16, 32 * 1024 * 1024, /* do_frees */ true);
+	do_allocs(32 * 1024* 1024, 16, /* do_frees */ true);
+	do_allocs(16, 32 * 1024 * 1024, /* do_frees */ false);
+	do_allocs(32 * 1024* 1024, 16, /* do_frees */ false);
+
+	return 0;
+}