On 12/19/25 16:58, Maxime Ripard wrote: > 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.
Completely agree, but that approach was rejected by the cgroups people. I mean we can already use udmabuf to allocate memcg accounted system memory which then can be imported into device drivers. So I don't see much reason why we should account dma-buf heaps and driver interfaces to memcg as well, we just need some way to limit them. Regards, Christian. > > Happy holidays, > Maxime
