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SubjectRe: [PATCH v2 1/2] procfs: Add 'size' to /proc/<pid>/fdinfo/
On Thu, Jun 23, 2022 at 03:06:06PM -0700, Kalesh Singh wrote:
> To be able to account the amount of memory a process is keeping pinned
> by open file descriptors add a 'size' field to fdinfo output.
>
> dmabufs fds already expose a 'size' field for this reason, remove this
> and make it a common field for all fds. This allows tracking of
> other types of memory (e.g. memfd and ashmem in Android).
>
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> Reviewed-by: Christian König <christian.koenig@amd.com>
> ---
>
> Changes in v2:
> - Add Christian's Reviewed-by
>
> Changes from rfc:
> - Split adding 'size' and 'path' into a separate patches, per Christian
> - Split fdinfo seq_printf into separate lines, per Christian
> - Fix indentation (use tabs) in documentaion, per Randy
>
> Documentation/filesystems/proc.rst | 12 ++++++++++--
> drivers/dma-buf/dma-buf.c | 1 -
> fs/proc/fd.c | 9 +++++----
> 3 files changed, 15 insertions(+), 7 deletions(-)
>
...
> diff --git a/fs/proc/fd.c b/fs/proc/fd.c
> index 913bef0d2a36..464bc3f55759 100644
> --- a/fs/proc/fd.c
> +++ b/fs/proc/fd.c
> @@ -54,10 +54,11 @@ static int seq_show(struct seq_file *m, void *v)
> if (ret)
> return ret;
>
> - seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\nino:\t%lu\n",
> - (long long)file->f_pos, f_flags,
> - real_mount(file->f_path.mnt)->mnt_id,
> - file_inode(file)->i_ino);
> + seq_printf(m, "pos:\t%lli\n", (long long)file->f_pos);
> + seq_printf(m, "flags:\t0%o\n", f_flags);
> + seq_printf(m, "mnt_id:\t%i\n", real_mount(file->f_path.mnt)->mnt_id);
> + seq_printf(m, "ino:\t%lu\n", file_inode(file)->i_ino);
> + seq_printf(m, "size:\t%lli\n", (long long)file_inode(file)->i_size);

Hi Kalesh,

Any reason not to use i_size_read() here?

Also not sure if it matters that much for your use case, but something
worth noting at least with shmem is that one can do something like:

# cat /proc/meminfo | grep Shmem:
Shmem: 764 kB
# xfs_io -fc "falloc -k 0 10m" ./file
# ls -alh file
-rw-------. 1 root root 0 Jun 28 07:22 file
# stat file
File: file
Size: 0 Blocks: 20480 IO Block: 4096 regular empty file
# cat /proc/meminfo | grep Shmem:
Shmem: 11004 kB

... where the resulting memory usage isn't reflected in i_size (but is
is in i_blocks/bytes).

Brian

>
> /* show_fd_locks() never deferences files so a stale value is safe */
> show_fd_locks(m, file, files);
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>

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