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

[Gabriel Krisman Bertazi <krisman@suse.de>]

Mohammed EL Kadiri <med08elkadiri@gmail.com> writes:

> 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>

Thanks!

>
> 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

This is desired behavior, IMO.  You should not lose casefold during a
remount, at risk of botching your data/splitting unrelated files. Also
this is the reason why I didn't expose it directly in /proc/mounts for
ovl, it would be easier but break the remount.

> 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/

Thanks for reporting and fixing this.  feel free to cc me on further
unicode stuff.  Will review it right now.

Thanks,

-- 
Gabriel Krisman Bertazi