Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Uladzislau Rezki <urezki@gmail.com>
Date:   Tue, 5 May 2020 13:03:20 +0200
To:     "Paul E. McKenney" <paulmck@kernel.org>,
        Joel Fernandes <joel@joelfernandes.org>
Cc:     Uladzislau Rezki <urezki@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Theodore Y . Ts'o" <tytso@mit.edu>,
        Matthew Wilcox <willy@infradead.org>,
        RCU <rcu@vger.kernel.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Subject: Re: [PATCH 09/24] rcu/tree: cache specified number of objects
Message-ID: <20200505110320.GA23774@pc636>
References: <20200428205903.61704-10-urezki@gmail.com>
 <20200501212749.GD7560@paulmck-ThinkPad-P72>
 <20200504124323.GA17577@pc636>
 <20200504152437.GK2869@paulmck-ThinkPad-P72>
 <20200504174822.GA20446@pc636>
 <20200504180805.GA172409@google.com>
 <20200504190138.GU2869@paulmck-ThinkPad-P72>
 <CAEXW_YQmrfbaDocsc7bLULRR1yUv4=MMMEw3b0s1mXM8sEVVzQ@mail.gmail.com>
 <20200504195128.GA21830@pc636>
 <20200504201641.GV2869@paulmck-ThinkPad-P72>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200504201641.GV2869@paulmck-ThinkPad-P72>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, May 04, 2020 at 01:16:41PM -0700, Paul E. McKenney wrote:
> On Mon, May 04, 2020 at 09:51:28PM +0200, Uladzislau Rezki wrote:
> > > > > Since we don't care about traversing backwards, isn't it better to use llist
> > > > > for this usecase?
> > > > >
> > > > > I think Vlad is using locking as we're also tracking the size of the llist to
> > > > > know when to free pages. This tracking could suffer from the lost-update
> > > > > problem without any locking, 2 lockless llist_add happened simulatenously.
> > > > >
> > > > > Also if list_head is used, it will take more space and still use locking.
> > > >
> > > > Indeed, it would be best to use a non-concurrent singly linked list.
> > > 
> > > Ok cool :-)
> > > 
> > > Is it safe to say something like the following is ruled out? ;-) :-D
> > > #define kfree_rcu_list_add llist_add
> > > 
> > In that case i think it is better just to add a comment about using
> > llist_head. To state that it used as a singular list to save space
> > and the access is synchronized by the lock :)
> > 
> > IMHO.
> 
> But adding such a comment would be fine as well.
> 
Thank you Paul and Joel!

--
Vlad Rezki