From: Rik van Riel <riel@xxxxxxxxxx> Always (and only) lock the root (oldest) anon_vma whenever we do something in an anon_vma. The recently introduced anon_vma scalability is due to the rmap code scanning only the VMAs that need to be scanned. Many common operations still took the anon_vma lock on the root anon_vma, so always taking that lock is not expected to introduce any scalability issues. However, always taking the same lock does mean we only need to take one lock, which means rmap_walk on pages from any anon_vma in the vma is excluded from occurring during an munmap, expand_stack or other operation that needs to exclude rmap_walk and similar functions. Also add the proper locking to vma_adjust. Signed-off-by: Rik van Riel <riel@xxxxxxxxxx> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> LKML-Reference: <20100526154044.2769e707@xxxxxxxxxxxxxxxxxxxxx> --- v3: - fix locking inversion in vma_adjust, spotted by Andrea - mm_take_all locks needs to use the bitflag in the root anon_vma, since that is the one that gets locked (Andrea Arcangeli) v2: - conditionally take the anon_vma lock in vma_adjust, like introduced in 252c5f94d944487e9f50ece7942b0fbf659c5c31 (with a proper comment) include/linux/rmap.h | 8 ++++---- mm/ksm.c | 2 +- mm/migrate.c | 2 +- mm/mmap.c | 30 ++++++++++++++++++++++-------- 4 files changed, 28 insertions(+), 14 deletions(-) Index: linux-2.6/include/linux/rmap.h =================================================================== --- linux-2.6.orig/include/linux/rmap.h +++ linux-2.6/include/linux/rmap.h @@ -104,24 +104,24 @@ static inline void vma_lock_anon_vma(str { struct anon_vma *anon_vma = vma->anon_vma; if (anon_vma) - spin_lock(&anon_vma->lock); + spin_lock(&anon_vma->root->lock); } static inline void vma_unlock_anon_vma(struct vm_area_struct *vma) { struct anon_vma *anon_vma = vma->anon_vma; if (anon_vma) - spin_unlock(&anon_vma->lock); + spin_unlock(&anon_vma->root->lock); } static inline void anon_vma_lock(struct anon_vma *anon_vma) { - spin_lock(&anon_vma->lock); + spin_lock(&anon_vma->root->lock); } static inline void anon_vma_unlock(struct anon_vma *anon_vma) { - spin_unlock(&anon_vma->lock); + spin_unlock(&anon_vma->root->lock); } /* Index: linux-2.6/mm/ksm.c =================================================================== --- linux-2.6.orig/mm/ksm.c +++ linux-2.6/mm/ksm.c @@ -325,7 +325,7 @@ static void drop_anon_vma(struct rmap_it { struct anon_vma *anon_vma = rmap_item->anon_vma; - if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->lock)) { + if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) { int empty = list_empty(&anon_vma->head); anon_vma_unlock(anon_vma); if (empty) Index: linux-2.6/mm/mmap.c =================================================================== --- linux-2.6.orig/mm/mmap.c +++ linux-2.6/mm/mmap.c @@ -506,6 +506,7 @@ int vma_adjust(struct vm_area_struct *vm struct vm_area_struct *importer = NULL; struct address_space *mapping = NULL; struct prio_tree_root *root = NULL; + struct anon_vma *anon_vma = NULL; struct file *file = vma->vm_file; long adjust_next = 0; int remove_next = 0; @@ -578,6 +579,17 @@ again: remove_next = 1 + (end > next-> } } + /* + * When changing only vma->vm_end, we don't really need anon_vma + * lock. This is a fairly rare case by itself, but the anon_vma + * lock may be shared between many sibling processes. Skipping + * the lock for brk adjustments makes a difference sometimes. + */ + if (vma->anon_vma && (insert || importer || start != vma->vm_start)) { + anon_vma = vma->anon_vma; + anon_vma_lock(anon_vma); + } + if (root) { flush_dcache_mmap_lock(mapping); vma_prio_tree_remove(vma, root); @@ -617,6 +629,8 @@ again: remove_next = 1 + (end > next-> __insert_vm_struct(mm, insert); } + if (anon_vma) + anon_vma_unlock(anon_vma); if (mapping) spin_unlock(&mapping->i_mmap_lock); @@ -2466,23 +2480,23 @@ static DEFINE_MUTEX(mm_all_locks_mutex); static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma) { - if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) { + if (!test_bit(0, (unsigned long *) &anon_vma->root->head.next)) { /* * The LSB of head.next can't change from under us * because we hold the mm_all_locks_mutex. */ - spin_lock_nest_lock(&anon_vma->lock, &mm->mmap_sem); + spin_lock_nest_lock(&anon_vma->root->lock, &mm->mmap_sem); /* * We can safely modify head.next after taking the - * anon_vma->lock. If some other vma in this mm shares + * anon_vma->root->lock. If some other vma in this mm shares * the same anon_vma we won't take it again. * * No need of atomic instructions here, head.next * can't change from under us thanks to the - * anon_vma->lock. + * anon_vma->root->lock. */ if (__test_and_set_bit(0, (unsigned long *) - &anon_vma->head.next)) + &anon_vma->root->head.next)) BUG(); } } @@ -2573,7 +2587,7 @@ out_unlock: static void vm_unlock_anon_vma(struct anon_vma *anon_vma) { - if (test_bit(0, (unsigned long *) &anon_vma->head.next)) { + if (test_bit(0, (unsigned long *) &anon_vma->root->head.next)) { /* * The LSB of head.next can't change to 0 from under * us because we hold the mm_all_locks_mutex. @@ -2584,10 +2598,10 @@ static void vm_unlock_anon_vma(struct an * * No need of atomic instructions here, head.next * can't change from under us until we release the - * anon_vma->lock. + * anon_vma->root->lock. */ if (!__test_and_clear_bit(0, (unsigned long *) - &anon_vma->head.next)) + &anon_vma->root->head.next)) BUG(); anon_vma_unlock(anon_vma); } Index: linux-2.6/mm/migrate.c =================================================================== --- linux-2.6.orig/mm/migrate.c +++ linux-2.6/mm/migrate.c @@ -682,7 +682,7 @@ skip_unmap: rcu_unlock: /* Drop an anon_vma reference if we took one */ - if (anon_vma && atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->lock)) { + if (anon_vma && atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) { int empty = list_empty(&anon_vma->head); anon_vma_unlock(anon_vma); if (empty) -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html