linux-kernel - Re: [PATCH v2] percpu: optimize locking in pcpu_balance

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Message-ID: <YMuo55c9QM91pc9p@casper.infradead.org>
Date:   Thu, 17 Jun 2021 20:56:23 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Roman Gushchin <guro@...com>
Cc:     Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] percpu: optimize locking in pcpu_balance_workfn()

On Thu, Jun 17, 2021 at 12:03:22PM -0700, Roman Gushchin wrote:
> +++ b/mm/percpu.c
> @@ -1980,6 +1980,9 @@ void __percpu *__alloc_reserved_percpu(size_t size, size_t align)
>   * If empty_only is %false, reclaim all fully free chunks regardless of the
>   * number of populated pages.  Otherwise, only reclaim chunks that have no
>   * populated pages.
> + *
> + * CONTEXT:
> + * pcpu_lock (can be dropped temporarily)
>   */

What's the shouting all about?  I would write it like this:

 * Context: Process context.  Caller must hold pcpu_lock with interrupts
 * disabled.  This function may drop the lock and re-enable interrupts if
 * it needs to sleep, but will return with the lock held and interrupts
 * disabled.