[0/3] shmem: Allow userspace monitoring of tmpfs for lack of space.

Message

Gabriel Krisman Bertazi March 22, 2022, 10:27 p.m. UTC

When provisioning containerized applications, multiple very small tmpfs
are used, for which one cannot always predict the proper file system
size ahead of time.  We want to be able to reliably monitor filesystems
for ENOSPC errors, without depending on the application being executed
reporting the ENOSPC after a failure.  It is also not enough to watch
statfs since that information might be ephemeral (say the application
recovers by deleting data, the issue can get lost).  For this use case,
it is also interesting to differentiate IO errors caused by lack of
virtual memory from lack of FS space.

This patch exposes two counters on sysfs that log the two conditions
that are interesting to observe for container provisioning.  They are
recorded per tmpfs superblock, and can be polled by a monitoring
application.

I proposed a more general approach [1] using fsnotify, but considering
the specificity of this use-case, people agreed it seems that a simpler
solution in sysfs is more than enough.

[1] https://lore.kernel.org/linux-mm/[e-mail]/T/#mee338d25b0e1e07cbe0861f9a5ca8cc439b3edb8

Gabriel Krisman Bertazi (3):
  shmem: Keep track of out-of-memory and out-of-space errors
  shmem: Introduce /sys/fs/tmpfs support
  shmem: Expose space and accounting error count

 Documentation/ABI/testing/sysfs-fs-tmpfs |  13 +++
 include/linux/shmem_fs.h                 |   7 ++
 mm/shmem.c                               | 103 ++++++++++++++++++++++-
 3 files changed, 121 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-fs-tmpfs