From: "J. Bruce Fields" <bfields@fieldses.org>
To: "Reshetova, Elena" <elena.reshetova@intel.com>
Cc: "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"jlayton@kernel.org" <jlayton@kernel.org>,
"trond.myklebust@primarydata.com"
<trond.myklebust@primarydata.com>,
"anna.schumaker@netapp.com" <anna.schumaker@netapp.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"keescook@chromium.org" <keescook@chromium.org>
Subject: Re: [PATCH 1/4] lockd: convert nlm_host.h_count from atomic_t to refcount_t
Date: Fri, 22 Dec 2017 10:42:50 -0500 [thread overview]
Message-ID: <20171222154250.GB9630@fieldses.org> (raw)
In-Reply-To: <20171222142553.GA9630@fieldses.org>
On Fri, Dec 22, 2017 at 09:25:53AM -0500, J. Bruce Fields wrote:
> On Fri, Dec 22, 2017 at 09:29:15AM +0000, Reshetova, Elena wrote:
> >
> > On Wed, Nov 29, 2017 at 01:15:43PM +0200, Elena Reshetova wrote:
> > > atomic_t variables are currently used to implement reference
> > > counters with the following properties:
> > > - counter is initialized to 1 using atomic_set()
> > > - a resource is freed upon counter reaching zero
> > > - once counter reaches zero, its further
> > > increments aren't allowed
> > > - counter schema uses basic atomic operations
> > > (set, inc, inc_not_zero, dec_and_test, etc.)
> >
> > >Whoops, I forgot that this doesn't apply to h_count.
> >
> > >Well, it's confusing, because h_count is actually used in two different
> > >ways: depending on whether a nlm_host represents a client or server, it
> > >may have the above properties or not.
> >
> >
> > So, what happens when it is not having the above properties? Is the object
> > being reused or?
>
> The object isn't destroyed when the counter hits zero--zero is just
> taken as a hint to some garbage collection algorithm that it would be OK
> to destroy it. So decrementing to or incrementing from zero is OK.
In more detail: the nlm_host objects that are used on the NFS server to
represent NFS clients are put by nlmsvc_release_host, and then may
eventually be freed by nlm_gc_hosts.
The nlm_host objects that are used on the NFS client to represent NFS
servers are put (and freed when h_count goes to zero) by
nlmclnt_release_host.
In both cases reference are taken by nlm_get_host. It would be possible
to replace nlm_get_host by two different functions if that would help.
Most callers are obviously only client-side or server-side. The only
exception is next_host_state. It could be passed a pointer to the "get"
function it should use.
After that we might actually just want to define separate client and
server structs like:
struct nlm_clnt_host {
struct nlm_host ch_host;
refcount_t ch_count;
...
}
struct nlm_srv_host {
struct nlm_host sh_host;
refcount_t sh_count;
...
}
rather than have a single h_count which is used in two confusingly
different ways. There are also some other nlm_host fields that really
only make sense for client or server.
--b.
next prev parent reply other threads:[~2017-12-22 15:42 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-29 11:15 [PATCH 0/4] lockd refcount conversions Elena Reshetova
2017-11-29 11:15 ` [PATCH 1/4] lockd: convert nlm_host.h_count from atomic_t to refcount_t Elena Reshetova
2017-12-21 20:23 ` J. Bruce Fields
2017-12-22 9:29 ` Reshetova, Elena
2017-12-22 14:25 ` J. Bruce Fields
2017-12-22 15:42 ` J. Bruce Fields [this message]
2017-12-27 12:10 ` Reshetova, Elena
2018-01-23 22:09 ` J. Bruce Fields
2018-01-24 0:47 ` Trond Myklebust
2018-01-24 21:09 ` J. Bruce Fields
2017-11-29 11:15 ` [PATCH 2/4] lockd: convert nsm_handle.sm_count " Elena Reshetova
2017-11-29 11:15 ` [PATCH 3/4] lockd: convert nlm_lockowner.count " Elena Reshetova
2017-11-29 11:15 ` [PATCH 4/4] lockd: convert nlm_rqst.a_count " Elena Reshetova
2017-11-29 22:23 ` [PATCH 0/4] lockd refcount conversions J. Bruce Fields
2017-11-30 7:48 ` Reshetova, Elena
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