[PATCH -v2 4/5] always lock the root (oldest) anon_vma
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From: Rik van Riel on 13 May 2010 10:40 > Looking at the if condition, brk() would appear to be the most important > case, right? This would appear to correlate with the reasoning behind > that condition in the first place in commit > 252c5f94d944487e9f50ece7942b0fbf659c5c31 where sbrk contended on the > lock heavily. You are right. Here is a new patch 4/5: --------------------- Subject: always lock the root (oldest) anon_vma 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(a)redhat.com> --- 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/mmap.c | 16 +++++++++++++++- 3 files changed, 20 insertions(+), 6 deletions(-) diff --git a/include/linux/rmap.h b/include/linux/rmap.h index 457ae1e..33ffe14 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -95,24 +95,24 @@ static inline void vma_lock_anon_vma(struct vm_area_struct *vma) { 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); } /* diff --git a/mm/ksm.c b/mm/ksm.c index d488012..7ca0dd7 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -325,7 +325,7 @@ static void drop_anon_vma(struct rmap_item *rmap_item) { struct anon_vma *anon_vma = rmap_item->anon_vma; - if (atomic_dec_and_lock(&anon_vma->ksm_refcount, &anon_vma->lock)) { + if (atomic_dec_and_lock(&anon_vma->ksm_refcount, &anon_vma->root->lock)) { int empty = list_empty(&anon_vma->head); anon_vma_unlock(anon_vma); if (empty) diff --git a/mm/mmap.c b/mm/mmap.c index f70bc65..a543359 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -506,6 +506,7 @@ int vma_adjust(struct vm_area_struct *vma, unsigned long start, 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; @@ -553,6 +554,17 @@ again: remove_next = 1 + (end > next->vm_end); } } + /* + * 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 (file) { mapping = file->f_mapping; if (!(vma->vm_flags & VM_NONLINEAR)) @@ -619,6 +631,8 @@ again: remove_next = 1 + (end > next->vm_end); if (mapping) spin_unlock(&mapping->i_mmap_lock); + if (anon_vma) + anon_vma_unlock(anon_vma); if (remove_next) { if (file) { @@ -2471,7 +2485,7 @@ static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma) * 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |