linux-kernel - Re: [patch] rewrite rd

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Message-Id: <200712040155.21124.rob@landley.net>
Date:	Tue, 4 Dec 2007 01:55:17 -0600
From:	Rob Landley <rob@...dley.net>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	Christian Borntraeger <borntraeger@...ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [patch] rewrite rd

On Monday 03 December 2007 22:26:28 Nick Piggin wrote:
> There is one slight downside -- direct block device access and filesystem
> metadata access goes through an extra copy and gets stored in RAM twice.
> However, this downside is only slight, because the real buffercache of the
> device is now reclaimable (because we're not playing crazy games with it),
> so under memory intensive situations, footprint should effectively be the
> same -- maybe even a slight advantage to the new driver because it can also
> reclaim buffer heads.

For the embedded world, initramfs has pretty much rendered initrd obsolete, 
and that was the biggest user of the ramdisk code I know of.  Beyond that, 
loopback mounts give you more flexible transient block devices than ramdisks 
do.  (In fact, ramdisks are such an amazing pain to use/size/free that if I 
really needed something like that I'd just make a loopback mount in a ramfs 
instance.)

Embedded users who still want a block interface for memory are generally 
trying to use a cramfs or squashfs image out of ROM or flash, although there 
are flash-specific filesystems for this and I dunno if they're actually 
mounting /dev/mem at an offset or something (md?  losetup -o?  Beats me, I 
haven't tried that myself yet...)

Rob
-- 
"One of my most productive days was throwing away 1000 lines of code."
  - Ken Thompson.
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