On Tue, Aug 06, 2024 at 04:09:43PM +0200, Maxime Ripard wrote: > On Tue, Aug 06, 2024 at 03:01:44PM GMT, Daniel Vetter wrote: > > On Mon, Jul 01, 2024 at 06:01:41PM +0100, Tvrtko Ursulin wrote: > > > > > > On 01/07/2024 10:25, Maarten Lankhorst wrote: > > > > Den 2024-06-28 kl. 16:04, skrev Maxime Ripard: > > > > > Hi, > > > > > > > > > > On Thu, Jun 27, 2024 at 09:22:56PM GMT, Maarten Lankhorst wrote: > > > > > > Den 2024-06-27 kl. 19:16, skrev Maxime Ripard: > > > > > > > Hi, > > > > > > > > > > > > > > Thanks for working on this! > > > > > > > > > > > > > > On Thu, Jun 27, 2024 at 05:47:21PM GMT, Maarten Lankhorst wrote: > > > > > > > > The initial version was based roughly on the rdma and misc cgroup > > > > > > > > controllers, with a lot of the accounting code borrowed from rdma. > > > > > > > > > > > > > > > > The current version is a complete rewrite with page counter; it uses > > > > > > > > the same min/low/max semantics as the memory cgroup as a result. > > > > > > > > > > > > > > > > There's a small mismatch as TTM uses u64, and page_counter long pages. > > > > > > > > In practice it's not a problem. 32-bits systems don't really come with > > > > > > > > > =4GB cards and as long as we're consistently wrong with units, it's > > > > > > > > fine. The device page size may not be in the same units as kernel page > > > > > > > > size, and each region might also have a different page size (VRAM vs GART > > > > > > > > for example). > > > > > > > > > > > > > > > > The interface is simple: > > > > > > > > - populate drmcgroup_device->regions[..] name and size for each active > > > > > > > > region, set num_regions accordingly. > > > > > > > > - Call drm(m)cg_register_device() > > > > > > > > - Use drmcg_try_charge to check if you can allocate a chunk of memory, > > > > > > > > use drmcg_uncharge when freeing it. This may return an error code, > > > > > > > > or -EAGAIN when the cgroup limit is reached. In that case a reference > > > > > > > > to the limiting pool is returned. > > > > > > > > - The limiting cs can be used as compare function for > > > > > > > > drmcs_evict_valuable. > > > > > > > > - After having evicted enough, drop reference to limiting cs with > > > > > > > > drmcs_pool_put. > > > > > > > > > > > > > > > > This API allows you to limit device resources with cgroups. > > > > > > > > You can see the supported cards in /sys/fs/cgroup/drm.capacity > > > > > > > > You need to echo +drm to cgroup.subtree_control, and then you can > > > > > > > > partition memory. > > > > > > > > > > > > > > > > Signed-off-by: Maarten Lankhorst<maarten.lankhorst@xxxxxxxxxxxxxxx> > > > > > > > > Co-developed-by: Friedrich Vock<friedrich.vock@xxxxxx> > > > > > > > I'm sorry, I should have wrote minutes on the discussion we had with TJ > > > > > > > and Tvrtko the other day. > > > > > > > > > > > > > > We're all very interested in making this happen, but doing a "DRM" > > > > > > > cgroup doesn't look like the right path to us. > > > > > > > > > > > > > > Indeed, we have a significant number of drivers that won't have a > > > > > > > dedicated memory but will depend on DMA allocations one way or the > > > > > > > other, and those pools are shared between multiple frameworks (DRM, > > > > > > > V4L2, DMA-Buf Heaps, at least). > > > > > > > > > > > > > > This was also pointed out by Sima some time ago here: > > > > > > > https://lore.kernel.org/amd-gfx/YCVOl8%2F87bqRSQei@phenom.ffwll.local/ > > > > > > > > > > > > > > So we'll want that cgroup subsystem to be cross-framework. We settled on > > > > > > > a "device" cgroup during the discussion, but I'm sure we'll have plenty > > > > > > > of bikeshedding. > > > > > > > > > > > > > > The other thing we agreed on, based on the feedback TJ got on the last > > > > > > > iterations of his series was to go for memcg for drivers not using DMA > > > > > > > allocations. > > > > > > > > > > > > > > It's the part where I expect some discussion there too :) > > > > > > > > > > > > > > So we went back to a previous version of TJ's work, and I've started to > > > > > > > work on: > > > > > > > > > > > > > > - Integration of the cgroup in the GEM DMA and GEM VRAM helpers (this > > > > > > > works on tidss right now) > > > > > > > > > > > > > > - Integration of all heaps into that cgroup but the system one > > > > > > > (working on this at the moment) > > > > > > > > > > > > Should be similar to what I have then. I think you could use my work to > > > > > > continue it. > > > > > > > > > > > > I made nothing DRM specific except the name, if you renamed it the device > > > > > > resource management cgroup and changed the init function signature to take a > > > > > > name instead of a drm pointer, nothing would change. This is exactly what > > > > > > I'm hoping to accomplish, including reserving memory. > > > > > > > > > > I've started to work on rebasing my current work onto your series today, > > > > > and I'm not entirely sure how what I described would best fit. Let's > > > > > assume we have two KMS device, one using shmem, one using DMA > > > > > allocations, two heaps, one using the page allocator, the other using > > > > > CMA, and one v4l2 device using dma allocations. > > > > > > > > > > So we would have one KMS device and one heap using the page allocator, > > > > > and one KMS device, one heap, and one v4l2 driver using the DMA > > > > > allocator. > > > > > > > > > > Would these make different cgroup devices, or different cgroup regions? > > > > > > > > Each driver would register a device, whatever feels most logical for that device I suppose. > > > > > > > > My guess is that a prefix would also be nice here, so register a device with name of drm/$name or v4l2/$name, heap/$name. I didn't give it much thought and we're still experimenting, so just try something. :) > > > > > > > > There's no limit to amount of devices, I only fixed amount of pools to match TTM, but even that could be increased arbitrarily. I just don't think there is a point in doing so. > > > > > > Do we need a plan for top level controls which do not include region names? > > > If the latter will be driver specific then I am thinking of ease of > > > configuring it all from the outside. Especially considering that one cgroup > > > can have multiple devices in it. > > > > > > Second question is about double accounting for shmem backed objects. I think > > > they will be seen, for drivers which allocate backing store at buffer > > > objects creation time, under the cgroup of process doing the creation, in > > > the existing memory controller. Right? > > > > We currently don't set __GFP_ACCOUNT respectively use GFP_KERNEL_ACCOUNT, > > so no. Unless someone allocates them with GFP_USER ... > > > > > Is there a chance to exclude those from there and only have them in this new > > > controller? Or would the opposite be a better choice? That is, not see those > > > in the device memory controller but only in the existing one. > > > > I missed this, so jumping in super late. I think guidance from Tejun was > > to go the other way around: Exclude allocations from normal system > > memory from device cgroups and instead make sure it's tracked in the > > existing memcg. > > > > Which might mean we need memcg shrinkers and the assorted pain ... > > > > Also I don't think we ever reached some agreement on where things like cma > > allocations should be accounted for in this case. > > Yeah, but that's the thing, memcg probably won't cut it for CMA. Because > if you pull the thread, that means that dma-heaps also have to register > their buffers into memcg too, even if it's backed by something else than > RAM. For cma I'm kinda leaning towards "both". If you don't have a special cma cgroup and just memcg, you can exhaust the cma easily. But if the cma allocations also aren't tracked in memcg, you have a blind spot there, which isn't great. > This is what this cgroup controller is meant to do: memcg for memory > (GFP'd) buffers, this cgroup for everything else. Yeah if there's no way you can get it through alloc_pages() it definitely shouldn't be in memcg. -Sima -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
