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Date:   Mon, 25 Jan 2021 14:22:36 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, RCU <rcu@vger.kernel.org>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Andrew Morton <akpm@linux-foundation.org>,
        Daniel Axtens <dja@axtens.net>,
        Frederic Weisbecker <frederic@kernel.org>,
        Neeraj Upadhyay <neeraju@codeaurora.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Theodore Y . Ts'o" <tytso@mit.edu>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Subject: Re: [PATCH 1/3] kvfree_rcu: Allocate a page for a single argument
Message-ID: <20210125132236.GJ827@dhcp22.suse.cz>
References: <20210120162148.1973-1-urezki@gmail.com>
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On Wed 20-01-21 17:21:46, Uladzislau Rezki (Sony) wrote:
> For a single argument we can directly request a page from a caller
> context when a "carry page block" is run out of free spots. Instead
> of hitting a slow path we can request an extra page by demand and
> proceed with a fast path.
> 
> A single-argument kvfree_rcu() must be invoked in sleepable contexts,
> and that its fallback is the relatively high latency synchronize_rcu().
> Single-argument kvfree_rcu() therefore uses GFP_KERNEL|__GFP_RETRY_MAYFAIL
> to allow limited sleeping within the memory allocator.

__GFP_RETRY_MAYFAIL can be quite heavy. It is effectively the most heavy
way to allocate without triggering the OOM killer. Is this really what
you need/want? Is __GFP_NORETRY too weak?

-- 
Michal Hocko
SUSE Labs