selftests/mm: vm_util: add helpers to set and restore shm limits

hugetlb-shm and thuge-gen tests require that limits defined by
/proc/sys/kernel/{shmmax,shmall} should be higher than certain values.

Add helpers that allow setting these limits and restoring their settings
on a test exit.

They will be used later in hugetlb-shm and thuge-gen.

Link: https://lore.kernel.org/20260511162840.375890-31-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Tested-by: Luiz Capitulino <luizcap@redhat.com>
Tested-by: Sarthak Sharma <sarthak.sharma@arm.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Donet Tom <donettom@linux.ibm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam Howlett <liam@infradead.org>
Cc: Li Wang <li.wang@linux.dev>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 37 insertions, 0 deletions

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 9256bbbe38ea..336a26751d3f 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -760,3 +760,31 @@ void write_num(const char *path, unsigned long num)
 	sprintf(buf, "%lu", num);
 	write_file(path, buf, strlen(buf) + 1);
 }
+
+static unsigned long shmall, shmmax;
+
+void __shm_limits_restore(void)
+{
+	if (shmmax)
+		write_num("/proc/sys/kernel/shmmax", shmmax);
+	if (shmall)
+		write_num("/proc/sys/kernel/shmall", shmall);
+}
+
+void shm_limits_prepare(unsigned long length)
+{
+	unsigned long nr = length / psize();
+	unsigned long val;
+
+	val = read_num("/proc/sys/kernel/shmmax");
+	if (val < length) {
+		write_num("/proc/sys/kernel/shmmax", length);
+		shmmax = val;
+	}
+
+	val = read_num("/proc/sys/kernel/shmall");
+	if (val < nr) {
+		write_num("/proc/sys/kernel/shmall", nr);
+		shmall = val;
+	}
+}
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 5fc9707f6b9a..ea8fc8fdf0eb 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -168,3 +168,12 @@ void write_file(const char *path, const char *buf, size_t buflen);
 int read_file(const char *path, char *buf, size_t buflen);
 unsigned long read_num(const char *path);
 void write_num(const char *path, unsigned long num);
+
+void shm_limits_prepare(unsigned long length);
+void __shm_limits_restore(void);
+
+#define SHM_LIMITS_RESTORE()						\
+static void __attribute__((destructor)) shm_limits_restore(void)	\
+{									\
+	__shm_limits_restore();						\
+}