On Wed, Nov 18, 2020 at 11:51 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > On Wed, Nov 18, 2020 at 11:32 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Wed 18-11-20 11:22:21, Suren Baghdasaryan wrote: > > > On Wed, Nov 18, 2020 at 11:10 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > > > > On Fri 13-11-20 18:16:32, Andrew Morton wrote: > > > > [...] > > > > > 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 am not sure TBH. Is there any reasonable usecase where uncoordinated > > > > memory tear down is OK and a target process which is able to see the > > > > unmapped memory? > > > > > > I think uncoordinated memory tear down is a special case which makes > > > sense only when the target process is being killed (and we can enforce > > > that by allowing MADV_DONTNEED to be used only if the target process > > > has pending SIGKILL). > > > > That would be safe but then I am wondering whether it makes sense to > > implement as a madvise call. It is quite strange to expect somebody call > > a syscall on a killed process. But this is more a detail. I am not a > > great fan of a more generic MADV_DONTNEED on a remote process. This is > > just too dangerous IMHO. > > Agree 100% I assumed here that by "a more generic MADV_DONTNEED on a remote process" you meant "process_madvise(MADV_DONTNEED) applied to a process that is not being killed". Re-reading your comment I realized that you might have meant "process_madvice() with generic support to large memory areas". I hope I understood you correctly. > > > > > > However, the ability to apply other flavors of > > > process_madvise() to large memory areas spanning multiple VMAs can be > > > useful in more cases. > > > > Yes I do agree with that. The error reporting would be more tricky but > > I am not really sure that the exact reporting is really necessary for > > advice like interface. > > Andrew's suggestion for this special mode to change return semantics > to the usual "0 or error code" seems to me like the most reasonable > way to deal with the return value limitation. > > > > > > For example in Android we will use > > > process_madvise(MADV_PAGEOUT) to "shrink" an inactive background > > > process. > > > > That makes sense to me. > > -- > > Michal Hocko > > SUSE Labs
