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charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Nov 5, 2020 at 9:44 AM Michal Hocko wrote: > > On Thu 05-11-20 09:21:13, Suren Baghdasaryan wrote: > > On Thu, Nov 5, 2020 at 9:16 AM Michal Hocko wrote: > > > > > > On Thu 05-11-20 08:50:58, Suren Baghdasaryan wrote: > > > > On Thu, Nov 5, 2020 at 4:20 AM Michal Hocko wrote: > > > > > > > > > > On Wed 04-11-20 12:40:51, Minchan Kim wrote: > > > > > > On Wed, Nov 04, 2020 at 07:58:44AM +0100, Michal Hocko wrote: > > > > > > > On Tue 03-11-20 13:32:28, Minchan Kim wrote: > > > > > > > > On Tue, Nov 03, 2020 at 10:35:50AM +0100, Michal Hocko wrote: > > > > > > > > > On Mon 02-11-20 12:29:24, Suren Baghdasaryan wrote: > > > > > > > > > [...] > > > > > > > > > > To follow up on this. Should I post an RFC implementing SIGKILL_SYNC > > > > > > > > > > which in addition to sending a kill signal would also reap the > > > > > > > > > > victim's mm in the context of the caller? Maybe having some code will > > > > > > > > > > get the discussion moving forward? > > > > > > > > > > > > > > > > > > Yeah, having a code, even preliminary, might help here. This definitely > > > > > > > > > needs a good to go from process management people as that proper is land > > > > > > > > > full of surprises... > > > > > > > > > > > > > > > > Just to remind a idea I suggested to reuse existing concept > > > > > > > > > > > > > > > > fd = pidfd_open(victim process) > > > > > > > > fdatasync(fd); > > > > > > > > close(fd); > > > > > > > > > > > > > > I must have missed this proposal. Anyway, are you suggesting fdatasync > > > > > > > to act as a destructive operation? > > > > > > > > > > > > write(fd) && fdatasync(fd) are already destructive operation if the file > > > > > > is shared. > > > > > > > > > > I am likely missing something because fdatasync will not destroy any > > > > > underlying data. It will sync > > > > > > > > > > > You don't need to reaping as destruptive operation. Rather than, just > > > > > > commit on the asynchrnous status "write file into page cache and commit > > > > > > with fsync" and "killing process and commit with fsync". > > > > > > > > > > I am sorry but I do not follow. The result of the memory reaping is a > > > > > data loss. Any private mapping will simply lose it's content. The caller > > > > > will get EFAULT when trying to access it but there is no way to > > > > > reconstruct the data. This is everything but not resembling what I see > > > > > f{data}sync is used for. > > > > > > > > I think Minchan considers f{data}sync as a "commit" operation. > > > > > > But there is nothing like commit in that operation. It is simply a > > > destroy operation. ftruncate as Minchan mentions in another reply would > > > be a closer fit but how do you interpret the length argument? What about > > > memory regions which cannot be reaped? > > > > > > I do understand that reusing an existing mechanism is usually preferable > > > but the semantic should be reasonable and easy to reason about. > > > > Maybe then we can consider a flag for pidfd_send_signal() to indicate > > that we want a synchronous mm cleanup when SIGKILL is being sent? > > Similar to my original RFC but cleanup would happen in the context of > > the caller. That seems to me like the simplest and most obvious way of > > expressing what we want to accomplish. WDYT? > > Yes that would make sense. Althought it would have to be SIGKILL > specific flag IMO. But let's see what process management people think > about that. Very well, I'll brush up the implementation and will post a new RFC. Thanks! > > -- > Michal Hocko > SUSE Labs