linux-kernel - Re: [PATCH] BC: resource beancounters (v2)

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Date:	Sat, 26 Aug 2006 13:55:43 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Andrew Morton <akpm@...l.org>, Kirill Korotaev <dev@...ru>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Pavel Emelianov <xemul@...nvz.org>,
	Andrey Savochkin <saw@...ru>, devel@...nvz.org,
	Rik van Riel <riel@...hat.com>, Andi Kleen <ak@...e.de>,
	Greg KH <greg@...ah.com>, Oleg Nesterov <oleg@...sign.ru>,
	Matt Helsley <matthltc@...ibm.com>,
	Rohit Seth <rohitseth@...gle.com>,
	Chandra Seetharaman <sekharan@...ibm.com>
Subject: Re: [PATCH] BC: resource beancounters (v2)

Alan Cox wrote:
> Ar Sad, 2006-08-26 am 01:14 +1000, ysgrifennodd Nick Piggin:
> 
>>I still think doing simple accounting per-page would be a better way to
>>go than trying to pin down all "user allocatable" kernel allocations.
>>And would require all of about 2 hooks in the page allocator. And would
>>track *actual* RAM allocated by that container.
> 
> 
> You have a variety of kernel objects you want to worry about and they
> have very differing properties.
> 
> Some are basically shared resources - page cache, dentries, inodes, etc
> and can be balanced pretty well by the kernel (ok the dentries are a bit
> of a problem right now). Others are very specific "owned" resources -
> like file handles, sockets and vmas.

That's true (OTOH I'd argue it would still be very useful for things
like pagecache, so one container can't start a couple of 'dd' loops
and turn everyone else to crap). And while the sharing may not be
exactly captured, statistically things should balance over time.

So I'm not arguing about _also_ accounting resources that are limited
in other ways (than just the RAM they consume).

But as a DoS protection measure on RAM usage, trying to account all
kernel allocations that are user triggerable just sounds hard to
maintain, holey, ugly, invsive (and not perfect either -- in fact it
still isn't clear to me that it is any better than my proposal).

> 
> Tracking actual RAM use by container/user/.. isn't actually that
> interesting. It's also inconveniently sub page granularity.

If it isn't interesting, then I don't think we want it (at least, until
someone does get an interest in it).

> 
> Its a whole seperate question whether you want a separate bean counter
> limit for sockets, file handles, vmas etc.

Yeah that's fair enough. We obviously want to avoid exposing limits on
things that it doesn't make sense to limit, or that is a kernel
implementation detail as much as possible.

eg. so I would be happy to limit virtual address, less happy to limit
vmas alone (unless that is in the context of accounting their RAM usage
or their implied vaddr charge).

-- 
SUSE Labs, Novell Inc.
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