linux-kernel - Re: [PATCH 4/8] mshare: selftests: Add test case shared memory

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Message-ID: <18530429-cac2-42a4-891e-24033dc54461@oracle.com>
Date: Thu, 28 Aug 2025 17:59:45 -0700
From: Anthony Yznaga <anthony.yznaga@...cle.com>
To: Yongting Lin <linyongting@...edance.com>, khalid@...nel.org,
        shuah@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        akpm@...ux-foundation.org, linux-mm@...ck.org
Subject: Re: [PATCH 4/8] mshare: selftests: Add test case shared memory

Hi Yongting,

Thank you for doing this. This is a great start for testing mshare.
I do have some comments below.

On 8/25/25 7:57 AM, Yongting Lin wrote:
> This test case aims to verify the basic functionalities of mshare.
> 
> Create a mshare file and use ioctl to create mapping for host mm
> with supportive flags, then create two processes to map mshare file
> to their memory spaces, and eventually verify the correctiness
> of sharing memory.
> 
> Signed-off-by: Yongting Lin <linyongting@...edance.com>
> ---
>   tools/testing/selftests/mshare/basic.c | 81 +++++++++++++++++++++++++-
>   1 file changed, 79 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/mshare/basic.c b/tools/testing/selftests/mshare/basic.c
> index 35739b1133f7..2347d30adfee 100644
> --- a/tools/testing/selftests/mshare/basic.c
> +++ b/tools/testing/selftests/mshare/basic.c
> @@ -3,9 +3,86 @@
>   #include "../kselftest_harness.h"
>   #include "util.c"
>   
> -TEST(basic)
> +#define STRING "I am Msharefs"
> +
> +FIXTURE(basic)
> +{
> +	char filename[128];
> +	size_t align_size;
> +	size_t allocate_size;
> +};
> +
> +FIXTURE_VARIANT(basic) {
> +	/* decide the time of real mapping size besed on align_size */
> +	size_t map_size_time;
> +	/* flags for ioctl */
> +	int map_flags;
> +};
> +
> +FIXTURE_VARIANT_ADD(basic, ANON_512G) {
> +	.map_size_time = 1,
> +	.map_flags = MAP_ANONYMOUS | MAP_SHARED | MAP_FIXED,
> +};
> +
> +FIXTURE_VARIANT_ADD(basic, HUGETLB_512G) {
> +	.map_size_time = 1,
> +	.map_flags = MAP_ANONYMOUS | MAP_HUGETLB | MAP_SHARED | MAP_FIXED,
> +};
> +
> +FIXTURE_VARIANT_ADD(basic, ANON_1T) {
> +	.map_size_time = 2,
> +	.map_flags = MAP_ANONYMOUS | MAP_SHARED | MAP_FIXED,
> +};
> +
> +FIXTURE_VARIANT_ADD(basic, HUGETLB_1T) {
> +	.map_size_time = 2,
> +	.map_flags = MAP_ANONYMOUS | MAP_HUGETLB | MAP_SHARED | MAP_FIXED,
> +};
> +
> +FIXTURE_SETUP(basic)
>   {
> -	printf("Hello mshare\n");
> +	int fd;
> +
> +	self->align_size = mshare_get_info();
> +	self->allocate_size = self->align_size * variant->map_size_time;
> +
> +	fd = create_mshare_file(self->filename, sizeof(self->filename));
> +	ftruncate(fd, self->allocate_size);
> +
> +	ASSERT_EQ(mshare_ioctl_mapping(fd, self->allocate_size, variant->map_flags), 0);

The tests should differentiate between how much VA space is allocated to 
an mshare region (i.e with ftruncate()) and how much memory is allocated 
within an mshare region through the ioctl. While the bounds of an mshare 
region need to be aligned to 512 GB, the memory allocated within it does 
not. Right now the tests will try to map 512 GB or 1 TB of anon or 
hugetlb memory in an mshare region which will fail on smaller systems to 
due to insufficient memory. Better to allocate smaller amounts so the 
tests can run on more systems.

Anthony

> +	close(fd);
> +}
> +
> +FIXTURE_TEARDOWN(basic)
> +{
> +	ASSERT_EQ(unlink(self->filename), 0);
> +}
> +
> +TEST_F(basic, shared_mem)
> +{
> +	int fd;
> +	void *addr;
> +	pid_t pid = fork();
> +
> +	ASSERT_NE(pid, -1);
> +
> +	fd = open(self->filename, O_RDWR, 0600);
> +	ASSERT_NE(fd, -1);
> +
> +	addr = mmap(NULL, self->allocate_size, PROT_READ | PROT_WRITE,
> +		       MAP_SHARED, fd, 0);
> +	ASSERT_NE(addr, MAP_FAILED);
> +
> +	if (pid == 0) {
> +		/* Child process write date the shared memory */
> +		memcpy(addr, STRING, sizeof(STRING));
> +		exit(0);
> +	}
> +
> +	ASSERT_NE(waitpid(pid, NULL, 0), -1);
> +
> +	/* Parent process should retrieve the data from the shared memory */
> +	ASSERT_EQ(memcmp(addr, STRING, sizeof(STRING)), 0);
>   }
>   
>   TEST_HARNESS_MAIN