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

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Date:	Tue, 9 Nov 2010 17:53:13 -0800
From:	Paul Menage <menage@...gle.com>
To:	Li Zefan <lizf@...fujitsu.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

On Tue, Nov 9, 2010 at 4:52 PM, Li Zefan <lizf@...fujitsu.com> wrote:
>>
>> bool active:1;
>> bool disabled:1;
>>
>
> It won't compile, but unsigned char active:1 will do. ;)

Are you sure? I don't have a buildable kernel tree at the moment, but
the following fragment compiled fine for me (with gcc 4.4.3):

struct foo {
  _Bool b1:1;
  _Bool b2:1;
};

and was sized at one byte. And "bool" is just a typedef of _Bool in
the kernel headers.

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

Agreed, within reason. But this patch doesn't reduce code size - it
makes the code fractionally more complicated and reduces the *binary*
size by a few bytes.

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

Replacing two function calls with one function call is a code
simplification and hence (generally) a good thing - the minuscule
reduction in binary size reduction that comes with it is just noise.

Paul
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