On Fri, Nov 13, 2020 at 5:18 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, 13 Nov 2020 17:09:37 -0800 Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > > > > > Seems to me that the ability to reap another process's memory is a > > > > > generally useful one, and that it should not be tied to delivering a > > > > > signal in this fashion. > > > > > > > > > > And we do have the new process_madvise(MADV_PAGEOUT). It may need a > > > > > few changes and tweaks, but can't that be used to solve this problem? > > > > > > > > Thank you for the feedback, Andrew. process_madvise(MADV_DONTNEED) was > > > > one of the options recently discussed in > > > > https://lore.kernel.org/linux-api/CAJuCfpGz1kPM3G1gZH+09Z7aoWKg05QSAMMisJ7H5MdmRrRhNQ@xxxxxxxxxxxxxx > > > > . The thread describes some of the issues with that approach but if we > > > > limit it to processes with pending SIGKILL only then I think that > > > > would be doable. > > > > > > Why would it be necessary to read /proc/pid/maps? I'd have thought > > > that a starting effort would be > > > > > > madvise((void *)0, (void *)-1, MADV_PAGEOUT) > > > > > > (after translation into process_madvise() speak). Which is equivalent > > > to the proposed process_madvise(MADV_DONTNEED_MM)? > > > > Yep, this is very similar to option #3 in > > https://lore.kernel.org/linux-api/CAJuCfpGz1kPM3G1gZH+09Z7aoWKg05QSAMMisJ7H5MdmRrRhNQ@xxxxxxxxxxxxxx > > and I actually have a tested prototype for that. > > Why is the `vector=NULL' needed? Can't `vector' point at a single iovec > which spans the whole address range? That would be the option #4 from the same discussion and the issues noted there are "process_madvise return value can't handle such a large number of bytes and there is MAX_RW_COUNT limit on max number of bytes one process_madvise call can handle". In my prototype I have a special handling for such "bulk operation" to work around the MAX_RW_COUNT limitation. > > > If that's the > > preferred method then I can post it quite quickly. > > I assume you've tested that prototype. How did its usefulness compare > with this SIGKILL-based approach? Just to make sure I understand correctly your question, you are asking about performance comparison of: // approach in this RFC pidfd_send_signal(SIGKILL, SYNC_REAP_MM) vs // option #4 in the previous RFC kill(SIGKILL); process_madvise(vector=NULL, MADV_DONTNEED); If so, I have results for the current RFC approach but the previous approach was testing on an older device, so don't have apples-to-apples comparison results at the moment. I can collect the data for fair comparison if desired, however I don't expect a noticeable performance difference since they both do pretty much the same thing (even on different devices my results are quite close). I think it's more a question of which API would be more appropriate. >
