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:   Mon, 4 May 2020 18:56:29 +0200
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     Uladzislau Rezki <urezki@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        LKML <linux-kernel@vger.kernel.org>, 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 19/24] rcu/tree: Support reclaim for head-less object
Message-ID: <20200504165629.GA20257@pc636>
References: <20200428205903.61704-1-urezki@gmail.com>
 <20200428205903.61704-20-urezki@gmail.com>
 <20200501223909.GF7560@paulmck-ThinkPad-P72>
 <20200504001258.GD197097@google.com>
 <20200504002855.GF2869@paulmck-ThinkPad-P72>
 <20200504003237.GD212435@google.com>
 <20200504142153.GG17577@pc636>
 <20200504153147.GL2869@paulmck-ThinkPad-P72>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200504153147.GL2869@paulmck-ThinkPad-P72>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

> > 
> > For single argument we can drop the lock before the entry to the page
> > allocator. Because it follows might_sleep() anotation we avoid of having
> > a situation when spinlock(rt mutex) is taken from any atomic context.
> > 
> > Since the lock is dropped the current context can be interrupted by
> > an IRQ which in its turn can also call kvfree_rcu() on current CPU.
> > In that case it must be double argument(single is not allowed) kvfree_rcu()
> > call. For PREEMPT_RT if no cache everything is reverted to rcu_head usage,
> > i.e. the entry to page allocator is bypassed.
> > 
> > It can be addressed as a separate patch and send out later on if we
> > are on the same page.
> > 
> > Paul, Joel what are your opinions?
> 
> I strongly prefer that it be removed from the series.  I do understand
> that this is a bit more hassle right now, but this does help avoid
> confusion in the future, plus perhaps also avoiding issues with future
> bisections.
> 
We have already decided to get rid of it, i mean small allocations(dynamic
rcu_head attaching). I will exclude it from next patch-set version. 

--
Vlad Rezki