linux-kernel - Re: Re: [BUG] ramfs system panic when using dd to create files

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Message-ID: <20210715114424.GR3809@techsingularity.net>
Date:   Thu, 15 Jul 2021 12:44:24 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     yong w <yongw.pur@...il.com>
Cc:     wuzhouhui <wuzhouhui14@...ls.ucas.ac.cn>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, nico@...xnic.net, wang.yong12@....com.cn
Subject: Re: Re: [BUG] ramfs system panic when using dd to create files

On Wed, Jul 14, 2021 at 10:30:22PM +0800, yong w wrote:
> Thanks for your reply!
> 
> > Limit max size of ramfs.
> It's no use using size to limit the size of ramfs.
> "mount -t ramfs -o size=10M ramfs /ramfs" is the command i use.
> 

ramfs does not support size= limiting, that's what tmpfs is for.

> >
> > The comments already explains why kernel should panic on this situation:
> >             /*
> >              * If we got here due to an actual allocation at the
> >              * system level, we cannot survive this and will enter
> >              * an endless loop in the allocator. Bail out now.
> >              */
>
> But it causes panic, actually , I don't want it panics

Then use tmpfs and specify size=. It's mentioned in filesystems/tmpfs.rst

--8<--
If you compare it to ramfs (which was the template to create tmpfs)
you gain swapping and limit checking. Another similar thing is the RAM
disk (/dev/ram*), which simulates a fixed size hard disk in physical
RAM, where you have to create an ordinary filesystem on top. Ramdisks
cannot swap and you do not have the possibility to resize them.
--8<--

-- 
Mel Gorman
SUSE Labs