linux-kernel - Re: [PATCH v2 1/1] mm/vmalloc: remove preempt

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Date:   Fri, 11 Oct 2019 23:56:42 +0200
From:   Daniel Wagner <dwagner@...e.de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Hillf Danton <hdanton@...a.com>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2 1/1] mm/vmalloc: remove preempt_disable/enable when do
 preloading



On 10/11/19 8:15 PM, Sebastian Andrzej Siewior wrote:
> On 2019-10-11 00:33:18 [+0200], Uladzislau Rezki (Sony) wrote:
>> Get rid of preempt_disable() and preempt_enable() when the
>> preload is done for splitting purpose. The reason is that
>> calling spin_lock() with disabled preemtion is forbidden in
>> CONFIG_PREEMPT_RT kernel.
>>
>> Therefore, we do not guarantee that a CPU is preloaded, instead
>> we minimize the case when it is not with this change.
>>
>> For example i run the special test case that follows the preload
>> pattern and path. 20 "unbind" threads run it and each does
>> 1000000 allocations. Only 3.5 times among 1000000 a CPU was
>> not preloaded. So it can happen but the number is negligible.
>>
>> V1 -> V2:
>>    - move __this_cpu_cmpxchg check when spin_lock is taken,
>>      as proposed by Andrew Morton
>>    - add more explanation in regard of preloading
>>    - adjust and move some comments
>>
>> Fixes: 82dd23e84be3 ("mm/vmalloc.c: preload a CPU with one object for split purpose")
>> Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
>> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> 
> Acked-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Acked-by: Daniel Wagner <dwagner@...e.de>