apparmor: global buffers spin lock may get contended

[John Johansen]

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 at 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 at canonical.com>
> 
> Reported-by: Sergey Senozhatsky <senozhatsky at chromium.org>

yep, thanks for catching that