On 10/20/2017 12:25 AM, 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()). > > 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 <[email protected]>
Acked-by: Vlastimil Babka <[email protected]> > --- > Changelog since v1: > - updated commit message > > mm/mlock.c | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/mm/mlock.c b/mm/mlock.c > index dfc6f1912176..3ceb2935d1e0 100644 > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -669,8 +669,6 @@ static __must_check int do_mlock(unsigned long start, > size_t len, vm_flags_t fla > if (!can_do_mlock()) > return -EPERM; > > - lru_add_drain_all(); /* flush pagevec */ > - > len = PAGE_ALIGN(len + (offset_in_page(start))); > start &= PAGE_MASK; > > @@ -797,9 +795,6 @@ SYSCALL_DEFINE1(mlockall, int, flags) > if (!can_do_mlock()) > return -EPERM; > > - if (flags & MCL_CURRENT) > - lru_add_drain_all(); /* flush pagevec */ > - > lock_limit = rlimit(RLIMIT_MEMLOCK); > lock_limit >>= PAGE_SHIFT; > >
