linux-kernel - Re: [PATCH 1/7] cgroups: Shrink struct cgroup

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Message-ID: <4CD9ECD2.3030805@cn.fujitsu.com>
Date:	Wed, 10 Nov 2010 08:52:34 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Paul Menage <menage@...gle.com>
CC:	"akpm >> Andrew Morton" <akpm@...ux-foundation.org>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	containers@...ts.linux-foundation.org
Subject: Re: [PATCH 1/7] cgroups: Shrink struct cgroup_subsys

Paul Menage wrote:
> On Sun, Nov 7, 2010 at 9:23 PM, Li Zefan <lizf@...fujitsu.com> wrote:
>> bool active;
>> bool disabled;
>> ...
>>
>> ?
>>
>> With alignment 5-8 bool values == 8 bytes in 64-bit machine, compared to
>> 4 bytes with the approach this patch takes.
> 
> I meant specifying it as:
> 
> bool active:1;
> bool disabled:1;
> 

It won't compile, but unsigned char active:1 will do. ;)

> i.e. keeping the bit-sized flags but also keeping the bool semantics.
> Having said that, I'm not really sure why saving 12 bytes per
> subsystem is worth a patch.

Every thing that reduces code size (without sacrifice readability
and maintain maintainability) should be worth.

This is one of the reasons we accept patches that replacing
kmalloc+memset with kzalloc, which just saves 8 bytes in my box.
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