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SubjectRe: [PATCH v2 1/2] procfs: Add 'size' to /proc/<pid>/fdinfo/
On Wed, Jun 29, 2022 at 5:23 AM Brian Foster <bfoster@redhat.com> wrote:
>
> On Tue, Jun 28, 2022 at 03:38:02PM -0700, Kalesh Singh wrote:
> > 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(-)
> > > >
> ...
> > >
> > > 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.
> >
>
> Sorry, it was implied in my previous test was that I was running against
> tmpfs. So regardless of fs, the fallocate keep_size semantics shown in
> both cases is as expected: the underlying blocks are allocated and the
> inode size is unchanged.
>
> What wasn't totally clear to me when I read this patch was 1. whether
> tmpfs refers to Shmem and 2. whether tmpfs allowed this sort of
> operation. The test above seems to confirm both, however, right? E.g., a
> more detailed example:
>
> # mount | grep /tmp
> tmpfs on /tmp type tmpfs (rw,nosuid,nodev,seclabel,nr_inodes=1048576,inode64)
> # cat /proc/meminfo | grep Shmem:
> Shmem: 5300 kB
> # xfs_io -fc "falloc -k 0 1g" /tmp/file
> # stat /tmp/file
> File: /tmp/file
> Size: 0 Blocks: 2097152 IO Block: 4096 regular empty file
> Device: 22h/34d Inode: 45 Links: 1
> Access: (0600/-rw-------) Uid: ( 0/ root) Gid: ( 0/ root)
> Context: unconfined_u:object_r:user_tmp_t:s0
> Access: 2022-06-29 08:04:01.301307154 -0400
> Modify: 2022-06-29 08:04:01.301307154 -0400
> Change: 2022-06-29 08:04:01.451312834 -0400
> Birth: 2022-06-29 08:04:01.301307154 -0400
> # cat /proc/meminfo | grep Shmem:
> Shmem: 1053876 kB
> # rm -f /tmp/file
> # cat /proc/meminfo | grep Shmem:
> Shmem: 5300 kB
>
> So clearly this impacts Shmem.. was your test run against tmpfs or some
> other (disk based) fs?

Hi Brian,

Thanks for clarifying. My issue was tmpfs not mounted at /tmp in my system:

==> meminfo.start <==
Shmem: 572 kB
==> meminfo.stop <==
Shmem: 51688 kB

>
> FWIW, I don't have any objection to exposing inode size if it's commonly
> useful information. My feedback was more just an fyi that i_size doesn't
> necessarily reflect underlying space consumption (whether it's memory or
> disk space) in more generic cases, because it sounds like that is really
> what you're after here. The opposite example to the above would be
> something like an 'xfs_io -fc "truncate 1t" /tmp/file', which shows a
> 1TB inode size with zero additional shmem usage.

From these cases, it seems the more generic way to do this is by
calculating the actual size consumed using the blocks. (i_blocks *
512). So in the latter example 'xfs_io -fc "truncate 1t" /tmp/file'
the size consumed would be zero. Let me know if it sounds ok to you
and I can repost the updated version.

Thanks,
Kalesh

>
> Brian
>
> > 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
> > > >
> > >
> >
>
> --
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>

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