Re: [PATCH v3 29/54] selftests/mm: vm_util: add helpers to set and restore shm limits

[Sarthak Sharma <sarthak.sharma@arm.com>]

On 4/29/26 2:12 AM, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> 
> 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.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Looks good to me.

Reviewed-by: Sarthak Sharma <sarthak.sharma@arm.com>

> ---
>  tools/testing/selftests/mm/vm_util.c | 28 ++++++++++++++++++++++++++++
>  tools/testing/selftests/mm/vm_util.h |  9 +++++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 752566f75c0b..5a89c2d903be 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -761,3 +761,31 @@ 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();						\
> +}