linux-kernel - Re: [PATCH 19/24] rcu/tree: Support reclaim for head-less object

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Message-ID: <20200504165629.GA20257@pc636>
Date:   Mon, 4 May 2020 18:56:29 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        RCU <rcu@...r.kernel.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH 19/24] rcu/tree: Support reclaim for head-less object

> > 
> > 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