perf bench mem: Switch from zalloc() to mmap()

Using mmap() ensures that the buffer is always aligned at a fixed
boundary. Switch to that to remove one source of variability.

Since we always want to read/write from the allocated buffers map
with pagetables pre-populated.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/bench/mem-functions.c

@@ -22,9 +22,9 @@
 #include <string.h>
 #include <unistd.h>
 #include <sys/time.h>
+#include <sys/mman.h>
 #include <errno.h>
 #include <linux/time64.h>
-#include <linux/zalloc.h>
 
 #define K 1024
 
@@ -286,16 +286,33 @@ static int do_memcpy(const struct function *r, struct bench_params *p,
 	return 0;
 }
 
+static void *bench_mmap(size_t size, bool populate)
+{
+	void *p;
+	int extra = populate ? MAP_POPULATE : 0;
+
+	p = mmap(NULL, size, PROT_READ|PROT_WRITE,
+		 extra | MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
+
+	return p == MAP_FAILED ? NULL : p;
+}
+
+static void bench_munmap(void *p, size_t size)
+{
+	if (p)
+		munmap(p, size);
+}
+
 static bool mem_alloc(struct bench_mem_info *info, struct bench_params *p,
 		      void **src, void **dst)
 {
 	bool failed;
 
-	*dst = zalloc(p->size);
+	*dst = bench_mmap(p->size, true);
 	failed = *dst == NULL;
 
 	if (info->alloc_src) {
-		*src = zalloc(p->size);
+		*src = bench_mmap(p->size, true);
 		failed = failed || *src == NULL;
 	}
 
@@ -306,8 +323,8 @@ static void mem_free(struct bench_mem_info *info __maybe_unused,
 		     struct bench_params *p __maybe_unused,
 		     void **src, void **dst)
 {
-	free(*dst);
-	free(*src);
+	bench_munmap(*dst, p->size);
+	bench_munmap(*src, p->size);
 
 	*dst = *src = NULL;
 }