On Thu, Apr 17, 2025 at 9:05 AM T.J. Mercier <tjmerc...@google.com> wrote: > > On Wed, Apr 16, 2025 at 9:56 PM Song Liu <s...@kernel.org> wrote: > > > > On Wed, Apr 16, 2025 at 7:09 PM T.J. Mercier <tjmerc...@google.com> wrote: > > > > > > On Wed, Apr 16, 2025 at 6:26 PM Song Liu <s...@kernel.org> wrote: > > [...] > > > > > > > > Here is another rookie question, it appears to me there is a file > > > > descriptor > > > > associated with each DMA buffer, can we achieve the same goal with > > > > a task-file iterator? > > > > > > That would find almost all of them, but not the kernel-only > > > allocations. (kernel_rss in the dmabuf_dump output I attached earlier. > > > If there's a leak, it's likely to show up in kernel_rss because some > > > driver forgot to release its reference(s).) Also wouldn't that be a > > > ton more iterations since we'd have to visit every FD to find the > > > small portion that are dmabufs? I'm not actually sure if buffers that > > > have been mapped, and then have had their file descriptors closed > > > would show up in task_struct->files; if not I think that would mean > > > scanning both files and vmas for each task. > > > > I don't think scanning all FDs to find a small portion of specific FDs > > is a real issue. We have a tool that scans all FDs in the system and > > only dump data for perf_event FDs. I think it should be easy to > > prototype a tool by scanning all files and all vmas. If that turns out > > to be very slow, which I highly doubt will be, we can try other > > approaches. > > But this will not find *all* the buffers, and that defeats the purpose > of having the iterator.
Do you mean this approach cannot get kernel only allocations? If that's the case, we probably do need a separate iterator. I am interested in other folks thoughts on this. > > OTOH, I am wondering whether we can build a more generic iterator > > for a list of objects. Adding a iterator for each important kernel lists > > seems not scalable in the long term. > > I think the wide variety of differences in locking for different > objects would make this difficult to do in a generic way. Agreed it is not easy to build a generic solution. But with the help from BTF, we can probably build something that covers a large number of use cases. Thanks, Song
