Messages in this thread | | | Date | Thu, 27 Jul 2023 15:42:58 +0200 | Subject | Re: [PATCH 16/17] cgroup/drm: Expose memory stats | From | Maarten Lankhorst <> |
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Hey,
On 2023-07-26 21:44, Tejun Heo wrote: > Hello, > > On Wed, Jul 26, 2023 at 12:14:24PM +0200, Maarten Lankhorst wrote: >>> So, yeah, if you want to add memory controls, we better think through how >>> the fd ownership migration should work. >> >> I've taken a look at the series, since I have been working on cgroup memory >> eviction. >> >> The scheduling stuff will work for i915, since it has a purely software >> execlist scheduler, but I don't think it will work for GuC (firmware) >> scheduling or other drivers that use the generic drm scheduler. >> >> For something like this, you would probably want it to work inside the drm >> scheduler first. Presumably, this can be done by setting a weight on each >> runqueue, and perhaps adding a callback to update one for a running queue. >> Calculating the weights hierarchically might be fun.. > > I don't have any idea on this front. The basic idea of making high level > distribution decisions in core code and letting individual drivers enforce > that in a way which fits them the best makes sense to me but I don't know > enough to have an opinion here. > >> I have taken a look at how the rest of cgroup controllers change ownership >> when moved to a different cgroup, and the answer was: not at all. If we > > For persistent resources, that's the general rule. Whoever instantiates a > resource gets to own it until the resource gets freed. There is an exception > with the pid controller and there are discussions around whether we want > some sort of migration behavior with memcg but yes by and large instantiator > being the owner is the general model cgroup follows. > >> attempt to create the scheduler controls only on the first time the fd is >> used, you could probably get rid of all the tracking. >> This can be done very easily with the drm scheduler. >> >> WRT memory, I think the consensus is to track system memory like normal >> memory. Stolen memory doesn't need to be tracked. It's kernel only memory, >> used for internal bookkeeping only. >> >> The only time userspace can directly manipulate stolen memory, is by mapping >> the pinned initial framebuffer to its own address space. The only allocation >> it can do is when a framebuffer is displayed, and framebuffer compression >> creates some stolen memory. Userspace is not >> aware of this though, and has no way to manipulate those contents. > > So, my dumb understanding: > > * Ownership of an fd can be established on the first ioctl call and doesn't > need to be migrated afterwards. There are no persistent resources to > migration on the first call. > > * Memory then can be tracked in a similar way to memcg. Memory gets charged > to the initial instantiator and doesn't need to be moved around > afterwards. There may be some discrepancies around stolen memory but the > magnitude of inaccuracy introduced that way is limited and bound and can > be safely ignored. > > Is that correct?
Hey,
Yeah mostly, I think we can stop tracking stolen memory. I stopped doing that for Xe, there is literally nothing to control for userspace in there.
Cheers, Maarten
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