On Tue, Apr 20, 2021 at 09:04:51AM +0200, Michal Hocko wrote: > On Mon 19-04-21 18:37:13, Christian König wrote: > > Am 19.04.21 um 18:11 schrieb Michal Hocko: > [...] > > > 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. > > > > No, not at all. The pages of a single DMA-buf could even be from different > > NUMA nodes if the exporting driver decides that this is somehow useful. > > As the use of the counter hasn't been explained yet I can only > speculate. One thing that I can imagine to be useful is to fill gaps in > our accounting. It is quite often that the memroy accounted in > /proc/meminfo (or oom report) doesn't add up to the overall memory > usage. In some workloads the workload can be huge! In many cases there > are other means to find out additional memory by a subsystem specific > interfaces (e.g. networking buffers). I do assume that dma-buf is just > one of those and the counter can fill the said gap at least partially > for some workloads. That is definitely useful.
A bit off-topic. Michal, I think it would have been nice to have an explanation like above in Documentation/proc/meminfo, what do you say? > What I am trying to bring up with NUMA side is that the same problem can > happen on per-node basis. Let's say that some user consumes unexpectedly > large amount of dma-buf on a certain node. This can lead to observable > performance impact on anybody on allocating from that node and even > worse cause an OOM for node bound consumers. How do I find out that it > was dma-buf that has caused the problem? > > See where I am heading? -- Sincerely yours, Mike.