lkml.org 
[lkml]   [2019]   [Feb]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: nbd, nbdkit, loopback mounts and memory management
On Fri, Feb 15, 2019 at 08:19:54PM +0100, Pavel Machek wrote:
> Hi!
>
> I watched fosdem talk about
> nbdkit... https://www.youtube.com/watch?v=9E5A608xJG0 . Nice. But word
> of warning: I'm not sure using it read-write on localhost is safe.
>
> In particular, user application could create a lot of dirty data
> quickly. If there's not enough memory for nbdkit (or nbd-client or
> nbd-server), you might get a deadlock.

Thanks for the kind words about the talk. I've added Wouter Verhelst
& the NBD mailing list to CC. Although I did the talk because the
subject is interesting, how I actually use nbdkit / NBD is to talk to
qemu and that's where I have most experience and where we (Red Hat)
use it in production systems.

However in January I spent a lot of time exercising the NBD loop-mount
+ nbdkit case using fio in order to find contention / bottlenecks in
our use of threads and locks. I didn't notice any particular problems
then, but it's possible my testing wasn't thorough enough. Or that
fio only creates small numbers of dirty pages (because of locality in
its access patterns I guess?)

When you say it's not safe, what could happen? What would we observe
if it was going wrong?

> Also note that nbd.txt in Documentation/blockdev/ points to
> sourceforge; it should probably point to
> https://github.com/NetworkBlockDevice/nbd ?

Wouter should be able to say what the correct link should be.

Rich.

--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines. Supports shell scripting,
bindings from many languages. http://libguestfs.org

\
 
 \ /
  Last update: 2019-02-15 23:42    [W:0.093 / U:27.108 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site