linux-kernel - Re: -mm merge plans for 2.6.26 (memcgroup)

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Message-Id: <20080420232427.1b399104.akpm@linux-foundation.org>
Date:	Sun, 20 Apr 2008 23:24:27 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	hugh@...itas.com, menage@...gle.com, balbir@...ux.vnet.ibm.com,
	xemul@...nvz.org, shiwh@...fujitsu.com, mel@....ul.ie,
	linux-kernel@...r.kernel.org
Subject: Re: -mm merge plans for 2.6.26 (memcgroup)

> On Mon, 21 Apr 2008 09:30:59 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> On Mon, 21 Apr 2008 00:51:30 +0100 (BST)
> Hugh Dickins <hugh@...itas.com> wrote:
> > >  disable-the-memory-controller-by-default-v3.patch
> > >  disable-the-memory-controller-by-default-v3-fix.patch
> > 
> > If those are to go in, then the sooner the better, yes.
> > 
> > But though I argued for cgroup_disable=memory (or some such),
> > I think myself that taking it even further now (requiring an
> > additional cgroup_enable=memory at boottime to get the memcg
> > stuff you chose with CGROUP_MEM_RES_CTLR=y at build time) is
> > confusing overkill, just messing around.

Yes, it does sound a bit silly.  I'd say just enable it, and provide a
cgroup_disable.

> > Others think differently.  A compromise would be to improve the
> > helptext for CGROUP_MEM_RES_CTLR (some of it is presently nonsense,
> > isn't it?  Certainly there's a significant overhead, but it's the
> > 32-bit struct page not the 64-bit which then suffers from crossing
> > cacheline boundaries).  Not much point in mentioning
> > cgroup_disable=memory if those patches go in, but needs to say
> > cgroup_enable=memory bootoption also needed.
> > 
> My concern around this is "default" action of cgroups may be different
> from each otther. It's confusing...
> 
> 
> > >  memcgroup-check-and-initialize-page-cgroup-in-memmap_init_zone.patch
> > 
> > No, it was a good find from Shi, but you were right to think the patch
> > fishy, and Kame put in lots of work (thank you!) to identify the actual
> > culprit: he and Mel are discussing what the actual fix should be; and
> > we might want to choose a different fix for stable than for 2.6.26.
> > 
> > I think you should drop that memmap_init_zone patch: the cgroup
> > pointer is not the only field we assume is zeroed, both flags and
> > mapping can cause trouble if they were not originally zeroed.
> > Re-zero the whole struct page?  No, far better to fix the
> > root of the corruption, that Kame and Mel are working on.
> > 
> I'll test and repodt Mel's patch later. I think Shi's patch will be
> unnecessary.

OK, I'll drop that one.

Thanks - it helps.

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