linux-kernel - Re: [PATCH -V2 0/9] memcg: add HugeTLB resource tracking

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Message-ID: <878vjgdvo4.fsf@linux.vnet.ibm.com>
Date:	Mon, 05 Mar 2012 00:45:55 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, mgorman@...e.de,
	kamezawa.hiroyu@...fujitsu.com, dhillf@...il.com,
	aarcange@...hat.com, mhocko@...e.cz, hannes@...xchg.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH -V2 0/9] memcg: add HugeTLB resource tracking

On Thu, 1 Mar 2012 14:40:29 -0800, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Thu,  1 Mar 2012 14:46:11 +0530
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
> 
> > This patchset implements a memory controller extension to control
> > HugeTLB allocations. It is similar to the existing hugetlb quota
> > support in that, the limit is enforced at mmap(2) time and not at
> > fault time. HugeTLB's quota mechanism limits the number of huge pages
> > that can allocated per superblock.
> > 
> > For shared mappings we track the regions mapped by a task along with the
> > memcg. We keep the memory controller charged even after the task
> > that did mmap(2) exits. Uncharge happens during truncate. For Private
> > mappings we charge and uncharge from the current task cgroup.
> 
> I haven't begin to get my head around this yet, but I'd like to draw
> your attention to https://lkml.org/lkml/2012/2/15/548.

Hmm that's really serious bug.

>  That fix has
> been hanging around for a while, but I haven't done anything with it
> yet because I don't like its additional blurring of the separation
> between hugetlb core code and hugetlbfs.  I want to find time to sit
> down and see if the fix can be better architected but haven't got
> around to that yet.
> 
> I expect that your patches will conflict at least mechanically with
> David's, which is not a big issue.  But I wonder whether your patches
> will copy the same bug into other places, and whether you can think of
> a tidier way of addressing the bug which David is seeing?
> 

I will go through the implementation again and make sure the problem
explained by David doesn't happen in the new code path added by the
patch series.

Thanks
-aneesh

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