Re: [PATCH] mm: anonymous shared memory naming

Kirill A. Shutemov
2022-11-06T13:34:03Z

On Sat, Nov 05, 2022 at 02:53:42AM +0000, Pasha Tatashin wrote:
> Since:
> commit 9a10064f5625 ("mm: add a field to store names for private anonymous
> memory")
>
> We can set names for private anonymous memory but not for shared
> anonymous memory. However, naming shared anonymous memory just as
> useful for tracking purposes.
>
> Extend the functionality to be able to set names for shared anon.
>
> / [anon_shmem:<name>] an anonymous shared memory mapping that has
> been named by userspace
>
> Sample output:
> share = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
> MAP_SHARED | MAP_ANONYMOUS, -1, 0);
> rv = prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME,
> share, SIZE, "shared anon");
>
> /proc/<pid>/maps (and smaps):
> 7fc8e2b4c000-7fc8f2b4c000 rw-s 00000000 00:01 1024
> /dev/zero (deleted) [anon_shmem:shared anon]
>
> pmap $(pgrep a.out)
> 254: pub/a.out
> 000056093fab2000 4K r---- a.out
> 000056093fab3000 4K r-x-- a.out
> 000056093fab4000 4K r---- a.out
> 000056093fab5000 4K r---- a.out
> 000056093fab6000 4K rw--- a.out
> 000056093fdeb000 132K rw--- [ anon ]
> 00007fc8e2b4c000 262144K rw-s- zero (deleted) [anon_shmem:shared anon]
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> Documentation/filesystems/proc.rst | 4 +++-
> fs/proc/task_mmu.c | 7 ++++---
> include/linux/mm.h | 2 ++
> include/linux/mm_types.h | 27 +++++++++++++--------------
> mm/madvise.c | 7 ++-----
> mm/shmem.c | 13 +++++++++++--
> 6 files changed, 35 insertions(+), 25 deletions(-)
>
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 898c99eae8e4..8f1e68460da5 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -431,8 +431,10 @@ is not associated with a file:
> [stack] the stack of the main process
> [vdso] the "virtual dynamic shared object",
> the kernel system call handler
> - [anon:<name>] an anonymous mapping that has been
> + [anon:<name>] a private anonymous mapping that has been
> named by userspace
> + path [anon_shmem:<name>] an anonymous shared memory mapping that has
> + been named by userspace

I expect it to break existing parsers. If the field starts with '/' it is
reasonable to assume the rest of the string to be a path, but it is not
the case now.

--
Kiryl Shutsemau / Kirill A. Shutemov