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

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Message-ID: <CAFuXZ_UY6RrOVmTayW-DdxQX9TE978LPx7ad=Pzr01j1cZ4o2Q@mail.gmail.com>
Date: Mon, 1 Sep 2025 20:50:47 +0800
From: Yongting Lin <linyongting@...edance.com>
To: Anthony Yznaga <anthony.yznaga@...cle.com>
Cc: khalid@...nel.org, shuah@...nel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, akpm@...ux-foundation.org, 
	linux-mm@...ck.org
Subject: Re: [External] Re: [PATCH 4/8] mshare: selftests: Add test case
 shared memory

On Fri, Aug 29, 2025 at 9:00 AM Anthony Yznaga
<anthony.yznaga@...cle.com> wrote:
>
> 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

I Changed my code to allocate a smaller chunk of memory (i.e.
4K/8K/2M/4M), and these tests are passed.

But I found something different:
step1:  ftruncate a mshare file to 512G
step2:  ioctl map 8K
step3: but after that, I am going to mmap 8K to a process but it
fails, then I have up to mmap 512G memory to process.
step4: Accessing the memory within the 8K boundary is fine but get
segfault after exceling the boundary (as the vma of host mm only holds
a memory region of 8K)

Should the mmap region keep consistent with the ioctl map region in
size? (currently, ioctl map region is 8K, but mmap region is 512G)

Yongting
>
> > +     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
>