On Wed, Jan 6, 2021 at 10:33 AM Namhyung Kim <namhy...@kernel.org> wrote: > > Hi Arnaldo, > > On Tue, Dec 29, 2020 at 8:51 PM Arnaldo Carvalho de Melo > <a...@kernel.org> wrote: > > > > Em Wed, Dec 16, 2020 at 06:05:56PM +0900, Namhyung Kim escreveu: > > > Currently it parses the /proc file everytime it opens a file in the > > > cgroupfs. Save the last result to avoid it (assuming it won't be > > > changed between the accesses). > > > > Which is the most likely case, but can't we use something like inotify > > to detect that and bail out or warn the user? > > Hmm.. looks doable. Will check.
So I've played with inotify a little bit, and it seems it needs to monitor changes on the file or the directory. I didn't get any notification from the /proc/mounts file even if I did some mount/umount. Instead, I could get IN_UNMOUNT when the cgroup filesystem was unmounted. But for the monitoring, we need to do one of a) select-like syscall to wait for the events, b) signal-driven IO notification or c) read the inotify file with non-block mode everytime. In a library code, I don't think we can do a) or b) since it can affect user program behaviors. Then we should go with c) but I think it's opposite to the purpose of this patch. :) As you said, I think mostly we don't care as the accesses will happen in a short period of time. But if you really care, maybe for the upcoming perf daemon changes, I think we can add an API to invalidate the cache or internal time-based invalidation logic (like remove it after 10 sec.). Thoughts? Thanks, Namhyung
