Re: [PATCH v2 1/2] procfs: Add 'size' to /proc/<pid>/fdinfo/

[Kalesh Singh <kaleshsingh@google.com>]

On Tue, Jun 28, 2022 at 4:54 AM Brian Foster <bfoster@redhat.com> wrote:
>
> 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?

Hi Brian.

Thanks for pointing this out. You are right, we should use
i_size_read() here. I'll update in the next version.

>
> 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).

I tried a similar experiment a few times, but I don't see the same
results. In my case, there is not any change in shmem. IIUC the
fallocate is allocating the disk space not shared memory.

cat /proc/meminfo > meminfo.start
xfs_io -fc "falloc -k 0 50m" ./xfs_file
cat /proc/meminfo > meminfo.stop
tail -n +1 meminfo.st* | grep -i '==\|Shmem:'

==> meminfo.start <==
Shmem:               484 kB
==> meminfo.stop <==
Shmem:               484 kB

ls -lh xfs_file
-rw------- 1 root root 0 Jun 28 15:12 xfs_file

stat xfs_file
  File: xfs_file
  Size: 0               Blocks: 102400     IO Block: 4096   regular empty file

Thanks,
Kalesh

>
> 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
> >
>