On Fri, Oct 20, 2017 at 9:25 AM, Shakeel Butt <shakeelb@xxxxxxxxxx> wrote: > lru_add_drain_all() is not required by mlock() and it will drain > everything that has been cached at the time mlock is called. And > that is not really related to the memory which will be faulted in > (and cached) and mlocked by the syscall itself. > > Without lru_add_drain_all() the mlocked pages can remain on pagevecs > and be moved to evictable LRUs. However they will eventually be moved > back to unevictable LRU by reclaim. So, we can safely remove > lru_add_drain_all() from mlock syscall. Also there is no need for > local lru_add_drain() as it will be called deep inside __mm_populate() > (in follow_page_pte()). > > On larger machines the overhead of lru_add_drain_all() in mlock() can > be significant when mlocking data already in memory. We have observed > high latency in mlock() due to lru_add_drain_all() when the users > were mlocking in memory tmpfs files. > > Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx> > --- I'm afraid I still don't fully understand the impact in terms of numbers and statistics as seen from inside a cgroup. My understanding is that we'll slowly see the unreclaimable stats go up as we drain the pvec's across CPU's I understand the optimization and I can see why lru_add_drain_all() is expensive. Acked-by: Balbir Singh <bsingharora@xxxxxxxxx> Balbir Singh. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
