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Date:   Fri, 25 Sep 2020 10:15:52 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Uladzislau Rezki <urezki@gmail.com>
Cc:     Mel Gorman <mgorman@techsingularity.net>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Michal Hocko <mhocko@suse.com>,
        LKML <linux-kernel@vger.kernel.org>, RCU <rcu@vger.kernel.org>,
        linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Theodore Y . Ts'o" <tytso@mit.edu>,
        Joel Fernandes <joel@joelfernandes.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>,
        Mel Gorman <mgorman@suse.de>
Subject: Re: [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func.
Message-ID: <20200925081552.GS2628@hirez.programming.kicks-ass.net>
References: <20200921160318.GO12990@dhcp22.suse.cz>
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 <20200923103706.GJ3179@techsingularity.net>
 <20200923154105.GO29330@paulmck-ThinkPad-P72>
 <20200923232251.GK3179@techsingularity.net>
 <20200924081614.GA14819@pc636>
 <20200924111907.GE2628@hirez.programming.kicks-ass.net>
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On Thu, Sep 24, 2020 at 05:21:12PM +0200, Uladzislau Rezki wrote:
> On Thu, Sep 24, 2020 at 01:19:07PM +0200, Peter Zijlstra wrote:
> > On Thu, Sep 24, 2020 at 10:16:14AM +0200, Uladzislau Rezki wrote:
> > > The key point is "enough". We need pages to make a) fast progress b) support
> > > single argument of kvfree_rcu(one_arg). Not vice versa. That "enough" depends
> > > on scheduler latency and vague pre-allocated number of pages, it might
> > > be not enough what would require to refill it more and more or we can overshoot
> > > that would lead to memory overhead. So we have here timing issues and
> > > not accurate model. IMHO.
> > 
> > I'm firmly opposed to the single argument kvfree_rcu() idea, that's
> > requiring memory to free memory.
> > 
> Hmm.. The problem is there is a demand in it:

People demand ponies all the time, the usual answer is: No.