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. 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. Thanks, Song
