linux-kernel - Re: apparmor: global buffers spin lock may get contended

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Date:   Sun, 30 Oct 2022 20:55:49 -0700
From:   John Johansen <john.johansen@...onical.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Tomasz Figa <tfiga@...omium.org>, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: apparmor: global buffers spin lock may get contended

On 10/30/22 20:52, Sergey Senozhatsky wrote:
> On (22/10/28 02:34), John Johansen wrote:
>>  From d026988196fdbda7234fb87bc3e4aea22edcbaf9 Mon Sep 17 00:00:00 2001
>> From: John Johansen <john.johansen@...onical.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@...onical.com>
> 
> Reported-by: Sergey Senozhatsky <senozhatsky@...omium.org>

yep, thanks for catching that