linux-kernel - Re: [PATCH v6] fork: free vmapped stacks in cache when cpus are offline

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Message-ID: <alpine.DEB.2.20.1702121623231.3734@nanos>
Date:   Sun, 12 Feb 2017 16:23:36 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Hoeun Ryu <hoeun.ryu@...il.com>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Mateusz Guzik <mguzik@...hat.com>,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v6] fork: free vmapped stacks in cache when cpus are
 offline

On Sun, 12 Feb 2017, Hoeun Ryu wrote:

>  Using virtually mapped stack, kernel stacks are allocated via vmalloc.
> In the current implementation, two stacks per cpu can be cached when
> tasks are freed and the cached stacks are used again in task duplications.
> but the cached stacks may remain unfreed even when cpu are offline.
>  By adding a cpu hotplug callback to free the cached stacks when a cpu
> goes offline, the pages of the cached stacks are not wasted.
> 
> Signed-off-by: Hoeun Ryu <hoeun.ryu@...il.com>
> Acked-by: Michal Hocko <mhocko@...e.com>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>