On Tuesday 04 December 2007 03:29:40 Nick Piggin wrote:
> On Tue, Dec 04, 2007 at 01:55:17AM -0600, Rob Landley wrote:
> > 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.)
>
> They are, although we could easily hook up a couple more ioctls for them
> now (if anybody is interested).
>From a usability perspective, an ioctl is no substitute for being able to
resize a device with "dd". (Or for that matter, make it sparse.)
> The rd driver can potentially be a _lot_ more scalable than the loop
> driver. It's completely lockless in the fastpath and doesn't even dirty any
> cachelines except for the actual destination memory. OK, this is only
> really important for testing purposes (eg. testing scalability of a
> filesystem etc.) But it is one reason why I (personally) want brd...
I wouldn't say not important: The "database in RAM" people will probably love
you, at least if they insist on using Oracle. (Filesystem schmilesystem,
gimme a raw block device and let me implement my own filesystem from
userspace...)
But I'm not personally likely to care. :)
> > 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...)
>
> OK, it would be interesting to hear from anyone using rd for things like
> cramfs.
I'd be interested in that too. I've heard it proposed a lot but not actually
seen anyone bother to implement it yet...
Rob
--
"One of my most productive days was throwing away 1000 lines of code."
- Ken Thompson.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
