linux-kernel - Re: [PATCH 1/2] Move kfree_call_rcu() to slab

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Date:   Thu, 4 Jan 2018 13:27:49 -0800
From:   Rao Shoaib <rao.shoaib@...cle.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org,
        paulmck@...ux.vnet.ibm.com, brouer@...hat.com, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] Move kfree_call_rcu() to slab_common.c



On 01/04/2018 12:35 PM, Rao Shoaib wrote:
> Hi Boqun,
>
> Thanks a lot for all your guidance and for catching the cut and paster 
> error. Please see inline.
>
>
> On 01/03/2018 05:38 PM, Boqun Feng wrote:
>>
>> But you introduced a bug here, you should use rcu_state_p instead of
>> &rcu_sched_state as the third parameter for __call_rcu().
>>
>> Please re-read:
>>
>>     https://marc.info/?l=linux-mm&m=151390529209639
>>
>> , and there are other comments, which you still haven't resolved in this
>> version. You may want to write a better commit log to explain the
>> reasons of each modifcation and fix bugs or typos in your previous
>> version. That's how review process works ;-)
>>
>> Regards,
>> Boqun
>>
> This is definitely a serious error. Thanks for catching this.
>
> As far as your previous comments are concerned, only the following one 
> has not been addressed. Can you please elaborate as I do not 
> understand the comment. The code was expanded because the new macro 
> expansion check fails. Based on Matthew Wilcox's comment I have 
> reverted rcu_head_name back to rcu_head.
It turns out I did not remember the real reason for the change. With the 
macro rewritten, using rcu_head as a macro argument does not work 
because it conflicts with the name of the type 'struct rcu_head' used in 
the macro. I have renamed the macro argument to rcu_name.

Shoaib
>
>> +#define kfree_rcu(ptr, rcu_head_name) \
>> +    do { \
>> +        typeof(ptr) __ptr = ptr;    \
>> +        unsigned long __off = offsetof(typeof(*(__ptr)), \
>> +                              rcu_head_name); \
>> +        struct rcu_head *__rptr = (void *)__ptr + __off; \
>> +        __kfree_rcu(__rptr, __off); \
>> +    } while (0)
>
> why do you want to open code this?
>
> Does the following text for the commit log looks better.
>
> kfree_rcu() should use the new kfree_bulk() interface for freeing rcu 
> structures
>
> The newly implemented kfree_bulk() interfaces are more efficient, 
> using the interfaces for freeing rcu structures has shown performance 
> improvements in synthetic benchmarks that allocate and free rcu 
> structures at a high rate.
>
> Shoaib
>
> -- 
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