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Date:   Mon, 31 Oct 2022 12:52:37 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     John Johansen <john.johansen@canonical.com>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Tomasz Figa <tfiga@chromium.org>, linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org
Subject: Re: apparmor: global buffers spin lock may get contended
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 <cfd5cc6f-5943-2e06-1dbe-f4b4ad5c1fa1@canonical.com>
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On (22/10/28 02:34), John Johansen wrote:
> From d026988196fdbda7234fb87bc3e4aea22edcbaf9 Mon Sep 17 00:00:00 2001
> From: John Johansen <john.johansen@canonical.com>
> Date: Tue, 25 Oct 2022 01:18:41 -0700
> Subject: [PATCH] apparmor: cache buffers on percpu list if there is lock
>  contention
> 
> On a heavily loaded machine there can be lock contention on the
> global buffers lock. Add a percpu list to cache buffers on when
> lock contention is encountered.
> 
> When allocating buffers attempt to use cached buffers first,
> before taking the global buffers lock. When freeing buffers
> try to put them back to the global list but if contention is
> encountered, put the buffer on the percpu list.
> 
> The length of time a buffer is held on the percpu list is dynamically
> adjusted based on lock contention.  The amount of hold time is rapidly
> increased and slow ramped down.
> 
> Signed-off-by: John Johansen <john.johansen@canonical.com>

Reported-by: Sergey Senozhatsky <senozhatsky@chromium.org>