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? > dma-buf is a device driver that provides a function so I might be > on the outside. However I also see that it might be relevant for a OOM. > It is memory that can be freed by killing userspace processes. > > The show_mem thing. Should it be a separate patch? This is up to you but if you want to expose the counter then send it in one series. -- Michal Hocko SUSE Labs
