On Fri 02-11-18 20:35:11, Vovo Yang wrote: > On Thu, Nov 1, 2018 at 9:10 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > OK, so that explain my question about the test case. Even though you > > generate a lot of page cache, the amount is still too small to trigger > > pagecache mostly reclaim and anon LRUs are scanned as well. > > > > Now to the difference with the previous version which simply set the > > UNEVICTABLE flag on mapping. Am I right assuming that pages are already > > at LRU at the time? Is there any reason the mapping cannot have the flag > > set before they are added to the LRU? > > I checked again. When I run gem_syslatency, it sets unevictable flag > first and then adds pages to LRU, so my explanation to the previous > test result is wrong. It should not be necessary to explicitly move > these pages to unevictable list for this test case. OK, that starts to make sense finally. > The performance > improvement of this patch on kbl might be due to not calling > shmem_unlock_mapping. Yes that one can get quite expensive. find_get_entries is really pointless here because you already do have your pages. Abstracting check_move_unevictable_pages into a pagevec api sounds like a reasonable compromise between the code duplication and relatively low-level api to export. > The perf result of a shmem lock test shows find_get_entries is the > most expensive part of shmem_unlock_mapping. > 85.32%--ksys_shmctl > shmctl_do_lock > --85.29%--shmem_unlock_mapping > |--45.98%--find_get_entries > | --10.16%--radix_tree_next_chunk > |--16.78%--check_move_unevictable_pages > |--16.07%--__pagevec_release > | --15.67%--release_pages > | --4.82%--free_unref_page_list > |--4.38%--pagevec_remove_exceptionals > --0.59%--_cond_resched -- Michal Hocko SUSE Labs
