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Tue, 29 Sep 2026 15:17:50 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 9oqPA57Wu2qXFQAAD6G6ig (envelope-from ); Tue, 29 Sep 2026 15:17:50 +0000 From: Gabriel Krisman Bertazi To: Mohammed EL Kadiri Cc: amir73il@gmail.com, brauner@kernel.org, danielzgtg.opensource@gmail.com, hughd@google.com, jack@suse.cz, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-unionfs@vger.kernel.org, miklos@szeredi.hu, tytso@mit.edu Subject: Re: [PATCH 1/4] shmem: Report casefold setting in mount options In-Reply-To: <20260929140011.211148-1-med08elkadiri@gmail.com> Organization: SUSE References: <20260928213155.2612039-1-krisman@suse.de> <20260928213155.2612039-2-krisman@suse.de> <20260929140011.211148-1-med08elkadiri@gmail.com> Date: Tue, 29 Sep 2026 11:17:48 -0400 Message-ID: <87pkxwxf1f.fsf@mailhost.krisman.be> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Action: no action X-Rspam-User: X-Stat-Signature: tb6gckijbabxjzzgz5ue5ukfismwdnoz X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 5AE6140006 X-HE-Tag: 1790695080-632768 X-HE-Meta: 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 +vRgtT3J jvvCY7Wg1Ig7G+BeXRvt7RKPzMozPcEqQM1hLzsjf/3uTpg57uQuSZ3iyQhY0hDYIAaRS5JKGRnQWMucGj09Jb6wvutZ2SBWpNIIGYAectyQVIdfs8x+42Ycx9oHDBnUD9NMXcqaFy1RlrMnAVogoDUW3rVe5dk5b9oADfv1DDcESFxWh20kMLY6KKsRohfLKBqewGNmOlR1OC6xud+gneVEWRwT+u4WjB1dnbujpBY0qVEg8RG3Tv8ZA09zsjdVjYfwx+In9GYpg86cXfw69am/ZErcoUVkJO7HKdUV/64Bw8r2uA9wjBZ/yqvtOc+V41RZ56FtDH6nyvt8Ty9zLbDmKX1OlmU9oh2s3kZIPX9MnMMHmY5Mjo2XC6xwZdcf3dAp1UqtLYKNtpTuuRESMSCfk2FrFvUTEIVo1WSrxpms0s8f2XWkJz7GWXw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Mohammed EL Kadiri 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 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