linux-kernel - Re: [PATCH] mm: clarify usage of GFP

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Message-ID: <875z7wjr26.fsf@nanos.tec.linutronix.de>
Date:   Tue, 29 Sep 2020 21:55:45 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        "Uladzislau Rezki \(Sony\)" <urezki@...il.com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm: clarify usage of GFP_ATOMIC in !preemptible contexts

On Tue, Sep 29 2020 at 14:30, Michal Hocko wrote:
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 67a0774e080b..2e8370cf60c7 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -238,7 +238,9 @@ struct vm_area_struct;
>   * %__GFP_FOO flags as necessary.
>   *
>   * %GFP_ATOMIC users can not sleep and need the allocation to succeed. A lower
> - * watermark is applied to allow access to "atomic reserves"
> + * watermark is applied to allow access to "atomic reserves".
> + * The current implementation doesn't support NMI and few other strict
> + * non-preemptive contexts (e.g. raw_spin_lock). The same applies to %GFP_NOWAIT.
>   *
>   * %GFP_KERNEL is typical for kernel-internal allocations. The caller requires
>   * %ZONE_NORMAL or a lower zone for direct access but can direct reclaim.

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