Re: [PATCH 1/4] shmem: Report casefold setting in mount options

[Mohammed EL Kadiri <med08elkadiri@gmail.com>]

On Mon, Sep 28, 2026 at 05:31:52PM -0400, Gabriel Krisman Bertazi wrote:
> For shmem, casefolding is a mount option.  Report the current encoding
> and casefolding flags in /proc/mounts

This works for me, on 90ddfbd19636 (akpm/mm-unstable), x86_64,
CONFIG_UNICODE=y:

  # mount -t tmpfs -o casefold tmpfs /t
  # grep /t /proc/mounts
  tmpfs /t tmpfs rw,relatime,casefold=utf8-12.1.0 0 0

Tested-by: Mohammed EL Kadiri <med08elkadiri@gmail.com>

Heads-up on one side effect, since mount(8) builds its remount options
from /proc/mounts: once casefold= is listed there, it gets passed back on
every remount.

  # mount -t tmpfs -o casefold tmpfs /t
  [  527.593309] tmpfs: Using encoding : utf8-12.1.0
  # mount -o remount,size=64M /t
  [  527.595716] tmpfs: Using encoding : utf8-12.1.0

That second line is shmem_parse_opt_casefold() running on a remount that
only asked to change size.  It calls utf8_load() each time, and nothing
frees the result - shmem_reconfigure() doesn't look at ctx->encoding and
shmem_free_fc() doesn't unload it.  50000 such remounts grew kmalloc-32 by
~50000 objects; a tmpfs without casefold stays flat.

The leak predates this patch - you can trigger it by passing casefold= on
a remount by hand - so I sent the fix as a separate patch:

https://lore.kernel.org/all/ba38f80f629fd093c77f3a49fdab7b71ee7bbc5f.1790687276.git.med08elkadiri@gmail.com/