selftests/mm: export get_free_hugepages()

Patch series "New selftest for mm", v2.

This is a simple test case that reproduces an mm problem[1], where a page
fault races with madvise(), and it is not trivial to reproduce and debug.

This test-case aims to avoid such race problems from happening again,
impacting workloads that leverages external allocators, such as tcmalloc,
jemalloc, etc.

[1] https://lore.kernel.org/all/20231001005659.2185316-1-riel@surriel.com/#r


This patch (of 2):

get_free_hugepages() is helpful for other hugepage tests.  Export it to
the common file (vm_util.c) to be reused.

Link: https://lkml.kernel.org/r/20231005163922.87568-1-leitao@debian.org
Link: https://lkml.kernel.org/r/20231005163922.87568-2-leitao@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Rik van Riel <riel@surriel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/hugetlb-madvise.c

@@ -36,25 +36,6 @@
 unsigned long huge_page_size;
 unsigned long base_page_size;
 
-unsigned long get_free_hugepages(void)
-{
-	unsigned long fhp = 0;
-	char *line = NULL;
-	size_t linelen = 0;
-	FILE *f = fopen("/proc/meminfo", "r");
-
-	if (!f)
-		return fhp;
-	while (getline(&line, &linelen, f) > 0) {
-		if (sscanf(line, "HugePages_Free:      %lu", &fhp) == 1)
-			break;
-	}
-
-	free(line);
-	fclose(f);
-	return fhp;
-}
-
 void write_fault_pages(void *addr, unsigned long nr_pages)
 {
 	unsigned long i;

tools/testing/selftests/mm/vm_util.c

@@ -269,3 +269,22 @@ int uffd_unregister(int uffd, void *addr, uint64_t len)
 
 	return ret;
 }
+
+unsigned long get_free_hugepages(void)
+{
+	unsigned long fhp = 0;
+	char *line = NULL;
+	size_t linelen = 0;
+	FILE *f = fopen("/proc/meminfo", "r");
+
+	if (!f)
+		return fhp;
+	while (getline(&line, &linelen, f) > 0) {
+		if (sscanf(line, "HugePages_Free:      %lu", &fhp) == 1)
+			break;
+	}
+
+	free(line);
+	fclose(f);
+	return fhp;
+}

tools/testing/selftests/mm/vm_util.h

@@ -51,6 +51,7 @@ int uffd_register(int uffd, void *addr, uint64_t len,
 int uffd_unregister(int uffd, void *addr, uint64_t len);
 int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 			      bool miss, bool wp, bool minor, uint64_t *ioctls);
+unsigned long get_free_hugepages(void);
 
 /*
  * On ppc64 this will only work with radix 2M hugepage size