On Mon, Apr 09, 2012 at 03:24:19PM +0400, Stanislav Kinsbursky wrote:07.04.2012 03:40, bfields@xxxxxxxxxxxx ÐÐÑÐÑ:On Fri, Apr 06, 2012 at 09:08:26PM +0400, Stanislav Kinsbursky wrote:Hello, Bruce.
Could you, please, clarify this reason why grace list is used?
I.e. why list is used instead of some atomic variable, for example?
Like just a reference count? Yeah, that would be OK.
In theory it could provide some sort of debugging help. (E.g. we could
print out the list of "lock managers" currently keeping us in grace.) I
had some idea we'd make those lock manager objects more complicated, and
might have more for individual containerized services.
Could you share this idea, please?
Anyway, I have nothing against lists. Just was curious, why it was used.
I added Trond and lists to this reply.
Let me explain, what is the problem with grace period I'm facing
right know, and what I'm thinking about it.
So, one of the things to be containerized during "NFSd per net ns"
work is the grace period, and these are the basic components of it:
1) Grace period start.
2) Grace period end.
3) Grace period check.
3) Grace period restart.
For restart, you're thinking of the fs/lockd/svc.c:restart_grace()
that's called on aisngal in lockd()?
I wonder if there's any way to figure out if that's actually used by
anyone? (E.g. by any distro init scripts). It strikes me as possibly
impossible to use correctly. Perhaps we could deprecate it....
So, the simplest straight-forward way is to make all internal stuff:
"grace_list", "grace_lock", "grace_period_end" work and both
"lockd_manager" and "nfsd4_manager" - per network namespace. Also,
"laundromat_work" have to be per-net as well.
In this case:
1) Start - grace period can be started per net ns in
"lockd_up_net()" (thus has to be moves there from "lockd()") and
"nfs4_state_start()".
2) End - grace period can be ended per net ns in "lockd_down_net()"
(thus has to be moved there from "lockd()"), "nfsd4_end_grace()" and
"fs4_state_shutdown()".
3) Check - looks easy. There is either svc_rqst or net context can
be passed to function.
4) Restart - this is a tricky place. It would be great to restart
grace period only for the networks namespace of the sender of the
kill signal. So, the idea is to check siginfo_t for the pid of
sender, then try to locate the task, and if found, then get sender's
networks namespace, and restart grace period only for this namespace
(of course, if lockd was started for this namespace - see below).
If it's really the signalling that's the problem--perhaps we can get
away from the signal-based interface.
At least in the case of lockd I suspect we could.
Or perhaps the decision to share a single lockd thread (or set of nsfd
threads) among multiple network namespaces was a poor one. But I
realize multithreading lockd doesn't look easy.