Re: [PATCH] dma-buf: system_heap: account for system heap allocation in memcg

[Maxime Ripard <mripard@redhat.com>]

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On Fri, Dec 19, 2025 at 02:50:50PM +0100, Christian König wrote:
> On 12/19/25 11:25, Maxime Ripard wrote:
> > On Mon, Dec 15, 2025 at 03:53:22PM +0100, Christian König wrote:
> >> On 12/15/25 14:59, Maxime Ripard wrote:
> ...
> >>>>> The shared ownership is indeed broken, but it's not more or less broken
> >>>>> than, say, memfd + udmabuf, and I'm sure plenty of others.
> >>>>>
> >>>>> So we really improve the common case, but only make the "advanced"
> >>>>> slightly more broken than it already is.
> >>>>>
> >>>>> Would you disagree?
> >>>>
> >>>> I strongly disagree. As far as I can see there is a huge chance we
> >>>> break existing use cases with that.
> >>>
> >>> Which ones? And what about the ones that are already broken?
> >>
> >> Well everybody that expects that driver resources are *not* accounted to memcg.
> > 
> > Which is a thing only because these buffers have never been accounted
> > for in the first place.
> 
> Yeah, completely agree. By not accounting it for such a long time we
> ended up with people depending on this behavior.
> 
> Not nice, but that's what it is.
> 
> > So I guess the conclusion is that we shouldn't
> > even try to do memory accounting, because someone somewhere might not
> > expect that one of its application would take too much RAM in the
> > system?
> 
> Well we do need some kind of solution to the problem. Either having
> some setting where you say "This memcg limit is inclusive/exclusive
> device driver allocated memory" or have a completely separate limit
> for device driver allocated memory.

A device driver memory specific limit sounds like a good idea because it
would make it easier to bridge the gap with dmem.

Happy holidays,
Maxime

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