linux-kernel - Re: RFC: Transparent Hugepage support

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Message-Id: <20091104093659.5de0e49d.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 4 Nov 2009 09:36:59 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	linux-mm@...ck.org, Marcelo Tosatti <mtosatti@...hat.com>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	Izik Eidus <ieidus@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Nick Piggin <npiggin@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: RFC: Transparent Hugepage support

On Tue, 3 Nov 2009 11:55:43 +0100
Andrea Arcangeli <aarcange@...hat.com> wrote:

> On Fri, Oct 30, 2009 at 09:40:37AM +0900, KAMEZAWA Hiroyuki wrote:
> > Ah, please keep CONFIG_TRANSPARENT_HUGEPAGE for a while.
> > Now, memcg don't handle hugetlbfs because it's special and cannot be freed by
> > the kernel, only users can free it. But this new transparent-hugepage seems to
> > be designed as that the kernel can free it for memory reclaiming.
> > So, I'd like to handle this in memcg transparently.
> > 
> > But it seems I need several changes to support this new rule.
> > I'm glad if this new huge page depends on !CONFIG_CGROUP_MEM_RES_CTRL for a
> > while.
> 
> Yeah the accounting (not just memcg) should be checked.. I didn't pay
> too much attention to stats at this point.
> 
> But we want to fix it fast instead of making the two options mutually
> exclusive.. Where are the pages de-accounted when they are freed?

It's de-accounted at page_remove_rmap() in typical case of Anon.
But swap-cache/bacthed-uncarhge related part is complicated, maybe.
...because of me ;(

Okay, I don't request !CONFIG_CGROUP_MEM_RES_CTRL, I'm glad if you CC me.

> Accounting seems to require just two one liners
> calling mem_cgroup_newpage_charge.
Yes, maybe so.

Thanks,
-Kame

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