linux-kernel - Re: [PATCH v6 2/2] init/do_mounts.c: create second mount for initramfs

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Date:   Fri, 17 Sep 2021 09:58:04 +0800
From:   Menglong Dong <menglong8.dong@...il.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>, johan@...nel.org,
        ojeda@...nel.org, jeyu@...nel.org, masahiroy@...nel.org,
        joe@...ches.com, Jan Kara <jack@...e.cz>, hare@...e.de,
        Jens Axboe <axboe@...nel.dk>, tj@...nel.org,
        gregkh@...uxfoundation.org, song@...nel.org,
        NeilBrown <neilb@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Barret Rhoden <brho@...gle.com>, f.fainelli@...il.com,
        palmerdabbelt@...gle.com, wangkefeng.wang@...wei.com,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>, vbabka@...e.cz,
        Alexander Potapenko <glider@...gle.com>,
        Petr Mladek <pmladek@...e.com>, johannes.berg@...el.com,
        "Eric W. Biederman" <ebiederm@...ssion.com>, jojing64@...il.com,
        terrelln@...com, geert@...ux-m68k.org,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Luis Chamberlain <mcgrof@...nel.org>, arnd@...db.de,
        Chris Down <chris@...isdown.name>, mingo@...nel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Josh Triplett <josh@...htriplett.org>
Subject: Re: [PATCH v6 2/2] init/do_mounts.c: create second mount for initramfs

Hello,

On Tue, Jul 27, 2021 at 8:37 PM Christian Brauner
<christian.brauner@...ntu.com> wrote:
[...]
>
> Yep, sorry.
> When I tested this early during the merge window it regressed booting a
> regular system for me meaning if I compiled a kernel with this feature
> enabled it complained about not being being able to open an initial
> console and it dropped me right into initramfs instead of successfully
> booting. I haven't looked into what this is caused or how to fix it for
> lack of time.

Our team has fully tested this feature, and no abnormalities have been
found yet.
What's more, this feature has been used in the product of our company. So if
there is any potential bug, as you mentioned above, I'd appreciate it if you can
spend some time on looking into it.

What's more, besides the problem that this feature solved, it has some more
benefits: saving memory. The amount of 'mnt_cache' is up to 50k when 180 docker
containers are created without this feature. However, only 15k 'mnt_cache' are
used with this feature enabled. Each 'mnt_cache' eats 320 bytes, so about 11M
memory is saved in this situation.

Please let me know if this feature is illogical or if there is any
better solution, thanks~

Best Wishes!
Menglong Dong