On Mon 19-04-21 17:44:13, Christian König wrote: > Am 19.04.21 um 17:19 schrieb Peter.Enderborg@xxxxxxxx: > > On 4/19/21 5:00 PM, Michal Hocko wrote: > > > On Mon 19-04-21 12:41:58, Peter.Enderborg@xxxxxxxx wrote: > > > > On 4/19/21 2:16 PM, Michal Hocko wrote: > > > > > On Sat 17-04-21 12:40:32, Peter Enderborg wrote: > > > > > > This adds a total used dma-buf memory. Details > > > > > > can be found in debugfs, however it is not for everyone > > > > > > and not always available. dma-buf are indirect allocated by > > > > > > userspace. So with this value we can monitor and detect > > > > > > userspace applications that have problems. > > > > > The changelog would benefit from more background on why this is needed, > > > > > and who is the primary consumer of that value. > > > > > > > > > > I cannot really comment on the dma-buf internals but I have two remarks. > > > > > Documentation/filesystems/proc.rst needs an update with the counter > > > > > explanation and secondly is this information useful for OOM situations > > > > > analysis? If yes then show_mem should dump the value as well. > > > > > > > > > > From the implementation point of view, is there any reason why this > > > > > hasn't used the existing global_node_page_state infrastructure? > > > > I fix doc in next version. Im not sure what you expect the commit message to include. > > > As I've said. Usual justification covers answers to following questions > > > - Why do we need it? > > > - Why the existing data is insuficient? > > > - Who is supposed to use the data and for what? > > > > > > I can see an answer for the first two questions (because this can be a > > > lot of memory and the existing infrastructure is not production suitable > > > - debugfs). But the changelog doesn't really explain who is going to use > > > the new data. Is this a monitoring to raise an early alarm when the > > > value grows? Is this for debugging misbehaving drivers? How is it > > > valuable for those? > > > > > > > The function of the meminfo is: (From Documentation/filesystems/proc.rst) > > > > > > > > "Provides information about distribution and utilization of memory." > > > True. Yet we do not export any random counters, do we? > > > > > > > Im not the designed of dma-buf, I think global_node_page_state as a kernel > > > > internal. > > > It provides a node specific and optimized counters. Is this a good fit > > > with your new counter? Or the NUMA locality is of no importance? > > Sounds good to me, if Christian Koenig think it is good, I will use that. > > It is only virtio in drivers that use the global_node_page_state if > > that matters. > > DMA-buf are not NUMA aware at all. On which node the pages are allocated > (and if we use pages at all and not internal device memory) is up to the > exporter and importer. The question is not whether it is NUMA aware but whether it is useful to know per-numa data for the purpose the counter is supposed to serve. -- Michal Hocko SUSE Labs
