On Fri, Nov 13, 2020 at 06:16:32PM -0800, Andrew Morton wrote: > On Fri, 13 Nov 2020 17:57:02 -0800 Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > > 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. > > Ah, OK, return value. Maybe process_madvise() shouldn't have done that > and should have simply returned 0 on success, like madvise(). > > I guess a special "nuke whole address space" command is OK. But, again > in the search for generality, the ability to nuke very large amounts of > address space (but not the entire address space) would be better. > > The process_madvise() return value issue could be addressed by adding a > process_madvise() mode which return 0 on success. > > And I guess the MAX_RW_COUNT issue is solvable by adding an > import_iovec() arg to say "don't check that". Along those lines. > > It's all sounding a bit painful (but not *too* painful). But to > reiterate, I do think that adding the ability for a process to shoot > down a large amount of another process's memory is a lot more generally > useful than tying it to SIGKILL, agree? I agree the direction but I think it's the general problem for every APIs have supported iovec and not sure process_madvise is special to chage it. IOW, it wouldn't be a problem to support *entire address space* special mode but not sure to support *large amount of address space* at the cost of breaking existing iovec scheme.
