On Thu, Dec 10, 2020 at 11:27:27AM +0100, Daniel Vetter wrote: > On Thu, Dec 10, 2020 at 11:10:45AM +0100, Greg KH wrote: > > On Thu, Dec 10, 2020 at 10:58:50AM +0100, Christian König wrote: > > > In general a good idea, but I have a few concern/comments here. > > > > > > Am 10.12.20 um 05:43 schrieb Hridya Valsaraju: > > > > This patch allows statistics to be enabled for each DMA-BUF in > > > > sysfs by enabling the config CONFIG_DMABUF_SYSFS_STATS. > > > > > > > > The following stats will be exposed by the interface: > > > > > > > > /sys/kernel/dmabuf/<inode_number>/exporter_name > > > > /sys/kernel/dmabuf/<inode_number>/size > > > > /sys/kernel/dmabuf/<inode_number>/dev_map_info > > > > > > > > The inode_number is unique for each DMA-BUF and was added earlier [1] > > > > in order to allow userspace to track DMA-BUF usage across different > > > > processes. > > > > > > > > Currently, this information is exposed in > > > > /sys/kernel/debug/dma_buf/bufinfo. > > > > However, since debugfs is considered unsafe to be mounted in production, > > > > it is being duplicated in sysfs. > > > > > > Mhm, this makes it part of the UAPI. What is the justification for this? > > > > > > In other words do we really need those debug information in a production > > > environment? > > > > Production environments seem to want to know who is using up memory :) > > This only shows shared memory, so it does smell a lot like $specific_issue > and we're designing a narrow solution for that and then have to carry it > forever. I think the "issue" is that this was a feature from ion that people "missed" in the dmabuf move. Taking away the ability to see what kind of allocations were being made didn't make a lot of debugging tools happy :( But Hridya knows more, she's been dealing with the transition for a long time now. > E.g. why is the list of attachments not a sysfs link? That's how we > usually expose struct device * pointers in sysfs to userspace, not as a > list of things. These aren't struct devices, so I don't understand the objection here. Where else could these go in sysfs? > Furthermore we don't have the exporter device covered anywhere, how is > that tracked? Yes Android just uses ion for all shared buffers, but that's > not how all of linux userspace works. Do we have the exporter device link in the dmabuf interface? If so, great, let's use that, but for some reason I didn't think it was there. > Then I guess there's the mmaps, you can fish them out of procfs. A tool > which collects all that information might be useful, just as demonstration > of how this is all supposed to be used. There's a script somewhere that does this today, again, Hridya knows more. > There's also some things to make sure we're at least having thought about > how other things fit in here. E.d. dma_resv attached to the dma-buf > matters in general a lot. It doesn't matter on Android because > everything's pinned all the time anyway. > > Also I thought sysfs was one value one file, dumping an entire list into > dev_info_map with properties we'll need to extend (once you care about > dma_resv you also want to know which attachments are dynamic) does not > smell like sysfs design at all. sysfs is one value per file, what is being exported that is larger than that here? Did I miss something on review? thanks, greg k-h
