linux-kernel - Re: [PATCH 1/5] memcg: export struct mem

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Message-Id: <20150715135711.1778a8c08f2ea9560a7c1f6f@linux-foundation.org>
Date:	Wed, 15 Jul 2015 13:57:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Tejun Heo <tj@...nel.org>, <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH 1/5] memcg: export struct mem_cgroup

On Wed, 15 Jul 2015 13:14:41 +0200 Michal Hocko <mhocko@...nel.org> wrote:

> mem_cgroup structure is defined in mm/memcontrol.c currently which
> means that the code outside of this file has to use external API even
> for trivial access stuff.
> 
> This patch exports mm_struct with its dependencies and makes some of the
> exported functions inlines. This even helps to reduce the code size a bit
> (make defconfig + CONFIG_MEMCG=y)
> 
> text		data    bss     dec     	 hex 	filename
> 12355346        1823792 1089536 15268674         e8fb42 vmlinux.before
> 12354970        1823792 1089536 15268298         e8f9ca vmlinux.after
> 
> This is not much (370B) but better than nothing. We also save a function
> call in some hot paths like callers of mem_cgroup_count_vm_event which is
> used for accounting.
> 
> The patch doesn't introduce any functional changes.
> 
> ...
>
>  include/linux/memcontrol.h | 369 +++++++++++++++++++++++++++++++++++++++++----

Boy, that's a ton of new stuff into the header file.  Do we actually
*need* to expose all this?  Is some other patch dependent on it?  If
not then perhaps we shouldn't do this - if the code was already this
way, I'd be attracted to a patch which was the reverse of this one!

There's some risk of build breakage here - just from a quick scan,
memcontrol.h is going to need eventfd.h for eventfd_ctx.  But what else
is needed?

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