From: Shakeel Butt <shakeelb@xxxxxxxxxx> Subject: mm: mlock: remove lru_add_drain_all() 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. 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. 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. [mhocko@xxxxxxxx: changelog fix] Link: http://lkml.kernel.org/r/20171019222507.2894-1-shakeelb@xxxxxxxxxx Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Acked-by: Balbir Singh <bsingharora@xxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Yisheng Xie <xieyisheng1@xxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Greg Thelen <gthelen@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/mlock.c | 5 ----- 1 file changed, 5 deletions(-) diff -puN mm/mlock.c~mm-mlock-remove-lru_add_drain_all mm/mlock.c --- a/mm/mlock.c~mm-mlock-remove-lru_add_drain_all +++ a/mm/mlock.c @@ -670,8 +670,6 @@ static __must_check int do_mlock(unsigne if (!can_do_mlock()) return -EPERM; - lru_add_drain_all(); /* flush pagevec */ - len = PAGE_ALIGN(len + (offset_in_page(start))); start &= PAGE_MASK; @@ -798,9 +796,6 @@ 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; _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
