linux-kernel - Re: [PATCH] ubifs: Add freeze support

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Message-ID: <b81dcdea-19d8-be73-057d-7059cf5fb3ab@nod.at>
Date:   Mon, 29 May 2017 12:17:00 +0200
From:   Richard Weinberger <richard@....at>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Hyunchul Lee <hyc.lee@...il.com>,
        Artem Bityutskiy <dedekind1@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, kernel-team@....com,
        linux-mtd@...ts.infradead.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] ubifs: Add freeze support

Amir,

Am 29.05.2017 um 12:04 schrieb Amir Goldstein:
>> Well, UBIFS is a bit different.
>> The UBIFS journal is not an add-on feature, you have to replay it in
>> any case. Otherwise you're facing corrupted data.
> 
> Yes, I suppose you are right.
> I guess there is no equivalent of mount -oro,{norecovery,noload} for
> ubifs.

Correct.

> I don't know the ubifs journal implementation details.
> Can ubifs_run_commit() when writers are frozen contribute to
> shorter journal replay time after boot with some workloads?

If the journal is empty then mounting will be faster, yes.
But I'm still interested in Hyunchul's use-case/problem.
Usually you run UBIFS in an embedded environment where you simple
never shutdown or reboot in a clean way. The power supply just
cut off.

On the other hand, if you want an empty journal for a faster mount,
just make sure that you umount upon shutdown.
Or make the size of the journal smaller at mkfs time.
Also see:

commit 27ad27993313312a4ad0047d0a944c425cd511a5
Author: Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
Date:   Thu Jan 29 16:34:30 2009 +0200

    UBIFS: remove fast unmounting

    This UBIFS feature has never worked properly, and it was a mistake
    to add it because we simply have no use-cases. So, lets still accept
    the fast_unmount mount option, but ignore it. This does not change
    much, because UBIFS commit in sync_fs anyway, and sync_fs is called
    while unmounting.

    Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@...ia.com>

Thanks,
//richard