linux-kernel - Re: [patch 1/3] mm: embed the memcg pointer directly into struct page

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Date:	Mon, 3 Nov 2014 10:09:42 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Tejun Heo <tj@...nel.org>, David Miller <davem@...emloft.net>,
	linux-mm@...ck.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/3] mm: embed the memcg pointer directly into struct page

Hi Joonsoo,

On Mon, Nov 03, 2014 at 05:02:08PM +0900, Joonsoo Kim wrote:
> On Sat, Nov 01, 2014 at 11:15:54PM -0400, Johannes Weiner wrote:
> > Memory cgroups used to have 5 per-page pointers.  To allow users to
> > disable that amount of overhead during runtime, those pointers were
> > allocated in a separate array, with a translation layer between them
> > and struct page.
> 
> Hello, Johannes.
> 
> I'd like to leave this translation layer.
> Could you just disable that code with #ifdef until next user comes?
> 
> In our company, we uses PAGE_OWNER on mm tree which is the feature
> saying who allocates the page. To use PAGE_OWNER needs modifying
> struct page and then needs re-compile. This re-compile makes us difficult
> to use this feature. So, we decide to implement run-time configurable
> PAGE_OWNER through page_cgroup's translation layer code. Moreover, with
> this infrastructure, I plan to implement some other debugging feature.
> 
> Because of my laziness, it didn't submitted to LKML. But, I will
> submit it as soon as possible. If the code is removed, I would
> copy-and-paste the code, but, it would cause lose of the history on
> that code. So if possible, I'd like to leave that code now.

Please re-introduce this code when your new usecase is ready to be
upstreamed.  There is little reason to burden an unrelated feature
with a sizable chunk of dead code for a vague future user.

Thanks
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