On Sun, Dec 2, 2012 at 7:12 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > Subject: [PATCH] mm/rmap, migration: Make rmap_walk_anon() and > try_to_unmap_anon() more scalable > > rmap_walk_anon() and try_to_unmap_anon() appears to be too > careful about locking the anon vma: while it needs protection > against anon vma list modifications, it does not need exclusive > access to the list itself. > > Transforming this exclusive lock to a read-locked rwsem removes > a global lock from the hot path of page-migration intense > threaded workloads which can cause pathological performance like > this: > > 96.43% process 0 [kernel.kallsyms] [k] perf_trace_sched_switch > | > --- perf_trace_sched_switch > __schedule > schedule > schedule_preempt_disabled > __mutex_lock_common.isra.6 > __mutex_lock_slowpath > mutex_lock > | > |--50.61%-- rmap_walk > | move_to_new_page > | migrate_pages > | migrate_misplaced_page > | __do_numa_page.isra.69 > | handle_pte_fault > | handle_mm_fault > | __do_page_fault > | do_page_fault > | page_fault > | __memset_sse2 > | | > | --100.00%-- worker_thread > | | > | --100.00%-- start_thread > | > --49.39%-- page_lock_anon_vma > try_to_unmap_anon > try_to_unmap > migrate_pages > migrate_misplaced_page > __do_numa_page.isra.69 > handle_pte_fault > handle_mm_fault > __do_page_fault > do_page_fault > page_fault > __memset_sse2 > | > --100.00%-- worker_thread > start_thread > > With this change applied the profile is now nicely flat > and there's no anon-vma related scheduling/blocking. Wouldn't the same reasoning apply to i_mmap_mutex ? Should we make that a rwsem as well ? I take it that Ingo's test case does not show this, but i_mmap_mutex's role with file pages is actually quite similar to the anon_vma lock with anon pages... -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- 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>