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>

1 files changed, 19 insertions, 0 deletions

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 558c9cd8901c..3082b40492dd 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/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;
+}