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mm: anonymous shared memory naming
Since commit 9a10064f ("mm: add a field to store names for private anonymous memory"), name for private anonymous memory, but not shared anonymous, can be set. However, naming shared anonymous memory just as useful for tracking purposes. Extend the functionality to be able to set names for shared anon. There are two ways to create anonymous shared memory, using memfd or directly via mmap(): 1. fd = memfd_create(...) mem = mmap(..., MAP_SHARED, fd, ...) 2. mem = mmap(..., MAP_SHARED | MAP_ANONYMOUS, -1, ...) In both cases the anonymous shared memory is created the same way by mapping an unlinked file on tmpfs. The memfd way allows to give a name for anonymous shared memory, but not useful when parts of shared memory require to have distinct names. Example use case: The VMM maps VM memory as anonymous shared memory (not private because VMM is sandboxed and drivers are running in their own processes). However, the VM tells back to the VMM how parts of the memory are actually used by the guest, how each of the segments should be backed (i.e. 4K pages, 2M pages), and some other information about the segments. The naming allows us to monitor the effective memory footprint for each of these segments from the host without looking inside the guest. Sample output: /* Create shared anonymous segmenet */ anon_shmem = mmap(NULL, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); /* Name the segment: "MY-NAME" */ rv = prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, anon_shmem, SIZE, "MY-NAME"); cat /proc/<pid>/maps (and smaps): 7fc8e2b4c000-7fc8f2b4c000 rw-s 00000000 00:01 1024 [anon_shmem:MY-NAME] If the segment is not named, the output is: 7fc8e2b4c000-7fc8f2b4c000 rw-s 00000000 00:01 1024 /dev/zero (deleted) Link: https://lkml.kernel.org/r/20221115020602.804224-1-pasha.tatashin@soleen.com Signed-off-by:Pasha Tatashin <pasha.tatashin@soleen.com> Acked-by: