On Thu, Oct 19, 2017 at 11:19 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > On Thu 19-10-17 15:25:07, Shakeel Butt 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()). > > This paragraph can be still a bit confusing. I suspect you meant to say > something like: "If anything lru_add_drain_all" should be called _after_ > pages have been mlocked and faulted in but even that is not strictly > needed because those pages would get to the appropriate LRUs lazily > during the reclaim path. Moreover follow_page_pte (gup) will drain the > local pcp LRU cache." > Andrew, can you please replace the second paragraph of the commit with Michal's suggested paragraph. >> 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> > > Anyway, this patch makes a lot of sense to me. Feel free to add > Acked-by: Michal Hocko <mhocko@xxxxxxxx> > Thanks. -- 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>
