August OpenZFS Leadership Meeting
Matthew Ahrens
mahrens at delphix.com
Fri Aug 23 18:26:43 UTC 2019
Thanks to everyone who participated at this month's meeting. We discussed
OpenZFS DevSummit talks; the Linux Plumbers Conference; 32-bit kernel
atomic reads; zfs share -a on Linux; and dedup improvements.
The video is available here: https://www.youtube.com/watch?v=zl4CUMOIi18
Notes (thanks Karyn):
-
OpenZFS DevSummit talks (matt)
-
Lots of great talks so far, but there is still room.
-
If you forgot to submit a talk before yesterday’s deadline, please
reach out right away. Matt will announce selected speakers in 2 weeks, so
there is a small grace period.
-
Registration is open now, and Matt will publicize this more once we
announce the speakers.
-
Linux Plumbers conf (Serapheim)
-
George WIlson and Serapheim will be at the Conference if you want to
talk ZFS or Debugging the Linux Kernel
-
If so, please reach out so the ZFS folks can meet up and talk about
all things ZFS.
-
OpenZFS on 32-bit architectures (relevant for FreeBSD, Linux, …): plain
reads of 64-bit “atomics” (Andriy)
-
Issue discovered: We use atomic operations to modify 64-bit values
that we treat as atomic, but to read them we use plain C assignment
operations, which works ok for 64-bit platforms, but not for
32-bit. Those
plain reads are implemented as 2 instructions there (32-bit), which is
incorrect.
-
At this point it is mostly theoretical (its is rare to hit a write
while crossing the 32-bit boundary) but it is still a valid concern.
-
The code paths are not very critical - mostly stats that we send to
user space.
-
Proposal for discussion: Should we introduce some kind of format
wrappers for those operations?
-
Paul Dagnelie: Has done some similar work for the SPL back in the
day and this should be straightforward.
-
Question: How many 32-bit platforms do we actually care for at
this point?
-
Andriy: Have heard of a few 32-bit Intel users out there
-
Tom Caputi: Has some experience for compile-time checks for
structures of these nature.
-
It seems like people are for it. Andriy will first talk with FreeBSD
developers, figure out how they want to proceed, and try to
propose designs
common for all platforms.
-
zfs share -a (George)
-
Issue: Stale file handles using zfs share -a and the sharenfs
property, by restarting or rebooting the nfs server.
-
The reason is that ZFS plugs into SystemD in a
cumbersome/non-natural way.
-
NFS shares actually start before the ZFS service. Mountd responds
to the client before the ZFS share is actually completed
leading to the
stale handles.
-
Hacky Approach:
-
Introduce a new component to zfs share. Instead of zfs share -a ,
zfs share -g (short for generate)
-
The idea is to add ZFS logic that ties it closer to NFS
-
Change of dependency ordering, zfs share -g generates the handles
for NFS, before NFS, and NFS consumes those generated handles.
-
Cons: A bit hacky for now
-
Pros: Simple and fast
-
Plan: To do more redesign on top of this for a cleaner solution
-
Others that have similar issues with George/Delphix feel free to
reach out.
-
Tom Caputi: Datto had issues with NFS in the past, and don't
use sharenfs, but they are interested on having control over this
functionality
-
Allan Jude: Seems like FreeBSD already does something similar,
so there may be some convergence of goals.
-
Submitted this as lightning talk at the Dev Summit
-
Anyone interested in working on implementing Matt’s ideas for dedup
ceiling and on disk format log (
http://open-zfs.org/w/images/8/8d/ZFS_dedup.pdf) please contact
allan at klarasystems.com to discuss. (Allan)
-
Problems using the feature for Terabytes of data due to known memory
issues
-
There is budget for a contract to implement the limit of the size of
the DDT proposed during one of the past Dev Summits
-
Feel free to reach out if you are interested in undertaking that work
On Mon, Aug 19, 2019 at 12:56 PM Matthew Ahrens <mahrens at delphix.com> wrote:
> The next OpenZFS Leadership meeting will be held tomorrow, August 20,
> 1pm-2pm Pacific time.
>
> Everyone is welcome to attend and participate, and we will try to keep the
> meeting on agenda and on time. The meetings will be held online via Zoom,
> and recorded and posted to the website and YouTube after the meeting.
>
> The agenda for the meeting will be a discussion of the projects listed in
> the agenda doc.
>
> For more information and details on how to attend, as well as notes and
> video from the previous meeting, please see the agenda document:
>
>
> https://docs.google.com/document/d/1w2jv2XVYFmBVvG1EGf-9A5HBVsjAYoLIFZAnWHhV-BM/edit
>
> --matt
>
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