On Wed, 25 Nov 2020 07:30:27 -0800 Shakeel Butt <shakeelb@xxxxxxxxxx> wrote: > On Tue, Oct 20, 2020 at 2:06 AM SeongJae Park <sjpark@xxxxxxxxxx> wrote: > > > > From: SeongJae Park <sjpark@xxxxxxxxx> > > > > Concurrent Idle Page Tracking users can interfere each other because the > > interface doesn't provide a central rule for synchronization between the > > users. Users could implement their own synchronization rule, but even > > in that case, applications developed by different users would not know > > how to synchronize with others. To help this situation, this commit > > introduces a centralized synchronization infrastructure of Idle Page > > Tracking. > > > > In detail, this commit introduces a mutex lock for Idle Page Tracking, > > called 'page_idle_lock'. It is exposed to user space via a new bool > > sysfs file, '/sys/kernel/mm/page_idle/lock'. By writing to and reading > > from the file, users can hold/release and read status of the mutex. > > Writes to the Idle Page Tracking 'bitmap' file fails if the lock is not > > held, while reads of the file can be done regardless of the lock status. > > > > Note that users could still interfere each other if they abuse this > > locking rule. Nevertheless, this change will let them notice the rule. > > > > Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx> > > I don't think this is allowed. I mean returning to user space with > held mutex and other processes can unlock it. I don't think mutex is > what you need. Or more importantly is this really an issue? > In a separate call, I and Shakeel agreed on that this is trying to fix an issue that aren't proved real. So I will drop this patch in next version of the patchset. We can restore this patch or find better fix later if the problem comes out in real. Thanks, SeongJae Park
