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 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. >
