From 4fc3f1d66b1ef0d7b8dc11f4ff1cc510f78b37d6 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Sun, 2 Dec 2012 19:56:50 +0000 Subject: 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. Rename anon_vma_[un]lock() => anon_vma_[un]lock_write(), to make it clearer that it's an exclusive write-lock in that case - suggested by Rik van Riel. Suggested-by: Linus Torvalds Cc: Peter Zijlstra Cc: Paul Turner Cc: Lee Schermerhorn Cc: Christoph Lameter Cc: Rik van Riel Cc: Mel Gorman Cc: Andrea Arcangeli Cc: Johannes Weiner Cc: Hugh Dickins Signed-off-by: Ingo Molnar Signed-off-by: Mel Gorman --- mm/ksm.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'mm/ksm.c') diff --git a/mm/ksm.c b/mm/ksm.c index ae539f0b8aa..7fa37de1ee0 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1634,7 +1634,7 @@ again: struct anon_vma_chain *vmac; struct vm_area_struct *vma; - anon_vma_lock(anon_vma); + anon_vma_lock_write(anon_vma); anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root, 0, ULONG_MAX) { vma = vmac->vma; @@ -1688,7 +1688,7 @@ again: struct anon_vma_chain *vmac; struct vm_area_struct *vma; - anon_vma_lock(anon_vma); + anon_vma_lock_write(anon_vma); anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root, 0, ULONG_MAX) { vma = vmac->vma; @@ -1741,7 +1741,7 @@ again: struct anon_vma_chain *vmac; struct vm_area_struct *vma; - anon_vma_lock(anon_vma); + anon_vma_lock_write(anon_vma); anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root, 0, ULONG_MAX) { vma = vmac->vma; -- cgit v1.2.3-18-g5258