linux-kernel - Re: [RFC][PATCH] memcg: change shmem handler.

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Message-Id: <20080703165604.a9be04bd.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 3 Jul 2008 16:56:04 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Balbir Singh <balbir@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] memcg: change shmem handler.

On Thu, 03 Jul 2008 12:45:14 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> > This patch fixes some mess by
> >   - PAGE_CGROUP_FLAG_CACHE is deleted (and replaced by FLAG_FILE)
> >   - PAGE_CGROUP_FLAG_SHMEM is added.
> >   - add_to_page_cache_nocharge() is added.
> >     This avoids mem_cgroup_charge_cache_page(). This is useful when page is
> >     pre-charged.
> >   - uses add_to_page_cache_nocharge() also in hugemem.
> >     (I think hugemem controller should be independent from memcg.
> >      Balbir, how do you think ?)
> 
> I am not 100% sure of that right now. I definitely want different control
> parameters (not included as a part of memory.limit_in_bytes). If there is
> leverage from memory controller, we could consider adding that to it or a
> separate controller if that makes more sense.
> 
Checking PG_compound in mem_cgroup_charge_cache_page() is enough, maybe.
(If multi-page-file-cache is added, need rework ;)

> >   - PageSwapBacked() is checked.
> >     (A imported patch from Hugh Dickins)
> > 
> > As result.
> >   - shmem will be in SwapBacked/Active list at first.
> 
> Good
> 
> >   - memcg has "shmem/tmpfs" counter.
> > 
> 
> I think this will be useful too (but I need to play with it)
> 
I've been argued that "if you want to add such a stupid counter, add the
same parameter to global lru without any overhead."

I'll postpone this ;) I have many other thing to do.

But the total number of pages used for shmem is already counted by
address_space->nr_pages. So, not very difficult for global lru if we can
walk all inodes of shmem. The problem will be "whether it's worth to do or not"

Thanks,
-Kame


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