From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755996AbdLVPmw (ORCPT ); Fri, 22 Dec 2017 10:42:52 -0500 Received: from fieldses.org ([173.255.197.46]:54552 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752063AbdLVPmv (ORCPT ); Fri, 22 Dec 2017 10:42:51 -0500 Date: Fri, 22 Dec 2017 10:42:50 -0500 From: "J. Bruce Fields" To: "Reshetova, Elena" Cc: "linux-nfs@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "jlayton@kernel.org" , "trond.myklebust@primarydata.com" , "anna.schumaker@netapp.com" , "peterz@infradead.org" , "keescook@chromium.org" Subject: Re: [PATCH 1/4] lockd: convert nlm_host.h_count from atomic_t to refcount_t Message-ID: <20171222154250.GB9630@fieldses.org> References: <1511954146-11793-1-git-send-email-elena.reshetova@intel.com> <1511954146-11793-2-git-send-email-elena.reshetova@intel.com> <20171221202350.GE31467@fieldses.org> <2236FBA76BA1254E88B949DDB74E612B802CFB57@IRSMSX102.ger.corp.intel.com> <20171222142553.GA9630@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171222142553.GA9630@fieldses.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.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.