selftests/vm: 8x compaction_test speedup

This patch reduces the running time for compaction_test from about 27 sec,
to 3.3 sec, which is about an 8x speedup.

These numbers are for an Intel x86_64 system with 32 GB of DRAM.

The compaction_test.c program was spending most of its time doing mmap(),
1 MB at a time, on about 25 GB of memory.

Instead, do the mmaps 100 MB at a time.  (Going past 100 MB doesn't make
things go much faster, because other parts of the program are using the
remaining time.)

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Sri Jayaramappa <sjayaram@akamai.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Link: https://lkml.kernel.org/r/20201002080621.551044-2-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/compaction_test.c

@@ -18,7 +18,8 @@
 
 #include "../kselftest.h"
 
-#define MAP_SIZE 1048576
+#define MAP_SIZE_MB	100
+#define MAP_SIZE	(MAP_SIZE_MB * 1024 * 1024)
 
 struct map_list {
 	void *map;
@@ -165,7 +166,7 @@ int main(int argc, char **argv)
 	void *map = NULL;
 	unsigned long mem_free = 0;
 	unsigned long hugepage_size = 0;
-	unsigned long mem_fragmentable = 0;
+	long mem_fragmentable_MB = 0;
 
 	if (prereq() != 0) {
 		printf("Either the sysctl compact_unevictable_allowed is not\n"
@@ -190,9 +191,9 @@ int main(int argc, char **argv)
 		return -1;
 	}
 
-	mem_fragmentable = mem_free * 0.8 / 1024;
+	mem_fragmentable_MB = mem_free * 0.8 / 1024;
 
-	while (mem_fragmentable > 0) {
+	while (mem_fragmentable_MB > 0) {
 		map = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE,
 			   MAP_ANONYMOUS | MAP_PRIVATE | MAP_LOCKED, -1, 0);
 		if (map == MAP_FAILED)
@@ -213,7 +214,7 @@ int main(int argc, char **argv)
 		for (i = 0; i < MAP_SIZE; i += page_size)
 			*(unsigned long *)(map + i) = (unsigned long)map + i;
 
-		mem_fragmentable--;
+		mem_fragmentable_MB -= MAP_SIZE_MB;
 	}
 
 	for (entry = list; entry != NULL; entry = entry->next) {