linux-kernel - Re: [PATCH RFC 01/10] rcu: Make CONFIG

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Message-ID: <f32ab99a-de28-b140-a7d0-027073055728@virtuozzo.com>
Date:   Wed, 8 Aug 2018 19:23:01 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Josh Triplett <josh@...htriplett.org>
Cc:     Michal Hocko <mhocko@...nel.org>, akpm@...ux-foundation.org,
        gregkh@...uxfoundation.org, rafael@...nel.org,
        viro@...iv.linux.org.uk, darrick.wong@...cle.com,
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        vivek.gautam@...eaurora.org, robin.murphy@....com, joe@...ches.com,
        heikki.krogerus@...ux.intel.com, sfr@...b.auug.org.au,
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        linux-mm@...ck.org
Subject: Re: [PATCH RFC 01/10] rcu: Make CONFIG_SRCU unconditionally enabled

On 08.08.2018 19:13, Josh Triplett wrote:
> On Wed, Aug 08, 2018 at 01:17:44PM +0300, Kirill Tkhai wrote:
>> On 08.08.2018 10:20, Michal Hocko wrote:
>>> On Tue 07-08-18 18:37:36, Kirill Tkhai wrote:
>>>> This patch kills all CONFIG_SRCU defines and
>>>> the code under !CONFIG_SRCU.
>>>
>>> The last time somebody tried to do this there was a pushback due to
>>> kernel tinyfication. So this should really give some numbers about the
>>> code size increase. Also why can't we make this depend on MMU. Is
>>> anybody else than the reclaim asking for unconditional SRCU usage?
>>
>> I don't know one. The size numbers (sparc64) are:
>>
>> $ size image.srcu.disabled 
>>    text	   data	    bss	    dec	    hex	filename
>> 5117546	8030506	1968104	15116156	 e6a77c	image.srcu.disabled
>> $ size image.srcu.enabled
>>    text	   data	    bss	    dec	    hex	filename
>> 5126175	8064346	1968104	15158625	 e74d61	image.srcu.enabled
>> The difference is: 15158625-15116156 = 42469 ~41Kb
> 
> 41k is a *substantial* size increase. However, can you compare
> tinyconfig with and without this patch? That may have a smaller change.

$ size image.srcu.disabled
   text	   data	    bss	    dec	    hex	filename
1105900	 195456	  63232	1364588	 14d26c	image.srcu.disabled

$ size image.srcu.enabled
   text	   data	    bss	    dec	    hex	filename
1106960	 195528	  63232	1365720	 14d6d8	image.srcu.enabled

1365720-1364588 = 1132 ~ 1Kb