Re: [RFC][PATCH 4/5] memcg: remove PCG_CACHE bit

[Johannes Weiner <hannes@cmpxchg.org>]

On Thu, Dec 15, 2011 at 03:08:22PM +0900, KAMEZAWA Hiroyuki wrote:
> >From 577b441ae259728d83a99baba11bf4925b4542d4 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Date: Thu, 15 Dec 2011 12:09:03 +0900
> Subject: [PATCH 4/5] memcg: remove PCG_CACHE bit.
> 
> This bit can be replaced by PageAnon(page) check.

You need to make sure that only fully rmapped pages are
charged/uncharged, which is not the case yet.  E.g. look at the
newpage_charge() in mm/memory.c::do_anonymous_page() - if the page
table is updated by someone else, that uncharge_page() in the error
path will see !PageAnon() because page->mapping is not set yet and
uncharge it as cache.

What I think is required is to break up the charging and committing
like we do for swap cache already:

	if (!mem_cgroup_try_charge())
		goto error;
	page_add_new_anon_rmap()
	mem_cgroup_commit()

This will also allow us to even get rid of passing around the charge
type everywhere...

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