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In-Reply-To: <20170823152542.5150-1-boqun.feng@gmail.com>
References: <20170823152542.5150-1-boqun.feng@gmail.com>
From: Arnd Bergmann <arnd@arndb.de>
Date: Wed, 23 Aug 2017 17:33:00 +0200
Message-ID: <CAK8P3a1FN8FoRNn8GYiPNTzAxGg_x+qkw5Z7eARTBirUkug2gQ@mail.gmail.com>
Subject: Re: [PATCH 0/2] completion: Reduce stack usage caused by COMPLETION_INITIALIZER_ONSTACK()
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Sender: owner-linux-mm@kvack.org
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To: Boqun Feng <boqun.feng@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Michel Lespinasse <walken@google.com>, Byungchul Park <byungchul.park@lge.com>, Andrew Morton <akpm@linux-foundation.org>, willy@infradead.org, Nicholas Piggin <npiggin@gmail.com>, kernel-team@lge.com

On Wed, Aug 23, 2017 at 5:25 PM, Boqun Feng <boqun.feng@gmail.com> wrote:
> With LOCKDEP_CROSSRELEASE and LOCKDEP_COMPLETIONS introduced, the growth
> in kernel stack usage of several functions were reported:
>
>         https://marc.info/?l=linux-kernel&m=150270063231284&w=2
>
> The root cause of this is in COMPLETION_INITIALIZER_ONSTACK(), we use
>
>         ({init_completion(&work); work})
>
> , which will create a temporary object when returned. However this
> temporary object is unnecessary. And this patch fixes it by making the
> statement expression in COMPLETION_INITIALIZER_ONSTACK() return a
> pointer rather than a whole structure. This will reduce the stack usage
> even if !LOCKDEP.
>
> However, such a change does make one COMPLETION_INITIALIZER_ONSTACK()
> callsite invalid, so we fix this first via converting to
> init_completion().

Both patches

Acked-by: Arnd Bergmann <arnd@arndb.de>

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