On Tue, Dec 15, 2020 at 3:57 AM SeongJae Park <sjpark@xxxxxxxxxx> wrote: > > From: SeongJae Park <sjpark@xxxxxxxxx> > > PG_idle and PG_young allow the two PTE Accessed bit users, Idle Page > Tracking and the reclaim logic concurrently work while don't interfere > each other. That is, when they need to clear the Accessed bit, they set > PG_young to represent the previous state of the bit, respectively. And > when they need to read the bit, if the bit is cleared, they further read > the PG_young to know whether the other has cleared the bit meanwhile or > not. > > We could add another page flag and extend the mechanism to use the flag > if we need to add another concurrent PTE Accessed bit user subsystem. > However, the space is limited. Meanwhile, if the new subsystem is > mutually exclusive with IDLE_PAGE_TRACKING or interfering with it is not > a real problem, it would be ok to simply reuse the PG_idle flag. > However, it's impossible because the flags are dependent on > IDLE_PAGE_TRACKING. > > To allow such reuse of the flags, this commit separates the PG_young and > PG_idle flag logic from IDLE_PAGE_TRACKING and introduces new kernel > config, 'PAGE_IDLE_FLAG'. Hence, a new subsystem would be able to reuse > PG_idle without depending on IDLE_PAGE_TRACKING. > > In the next commit, DAMON's reference implementation of the virtual > memory address space monitoring primitives will use it. > > Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
