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

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Date:   Thu, 4 Jan 2018 12:35:55 -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

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.

> +#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