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/huge_memory.c | 6 +++--- mm/ksm.c | 6 +++--- mm/memory-failure.c | 4 ++-- mm/migrate.c | 2 +- mm/mmap.c | 2 +- mm/mremap.c | 2 +- mm/rmap.c | 48 ++++++++++++++++++++++++------------------------ 7 files changed, 35 insertions(+), 35 deletions(-) (limited to 'mm') diff --git a/mm/huge_memory.c b/mm/huge_memory.c index acd37fe..a24c9cb 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1549,7 +1549,7 @@ int split_huge_page(struct page *page) int ret = 1; BUG_ON(!PageAnon(page)); - anon_vma = page_lock_anon_vma(page); + anon_vma = page_lock_anon_vma_read(page); if (!anon_vma) goto out; ret = 0; @@ -1562,7 +1562,7 @@ int split_huge_page(struct page *page) BUG_ON(PageCompound(page)); out_unlock: - page_unlock_anon_vma(anon_vma); + page_unlock_anon_vma_read(anon_vma); out: return ret; } @@ -2074,7 +2074,7 @@ static void collapse_huge_page(struct mm_struct *mm, if (!pmd_present(*pmd) || pmd_trans_huge(*pmd)) goto out; - anon_vma_lock(vma->anon_vma); + anon_vma_lock_write(vma->anon_vma); pte = pte_offset_map(pmd, address); ptl = pte_lockptr(mm, pmd); diff --git a/mm/ksm.c b/mm/ksm.c index ae539f0..7fa37de 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; diff --git a/mm/memory-failure.c b/mm/memory-failure.c index ddb68a1..f2cd830 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -402,7 +402,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill, struct anon_vma *av; pgoff_t pgoff; - av = page_lock_anon_vma(page); + av = page_lock_anon_vma_read(page); if (av == NULL) /* Not actually mapped anymore */ return; @@ -423,7 +423,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill, } } read_unlock(&tasklist_lock); - page_unlock_anon_vma(av); + page_unlock_anon_vma_read(av); } /* diff --git a/mm/migrate.c b/mm/migrate.c index f24e9cc..6e46485 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -754,7 +754,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage, */ if (PageAnon(page)) { /* - * Only page_lock_anon_vma() understands the subtleties of + * Only page_lock_anon_vma_read() understands the subtleties of * getting a hold on an anon_vma from outside one of its mms. */ anon_vma = page_get_anon_vma(page); diff --git a/mm/mmap.c b/mm/mmap.c index 8840863..68a16b4 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -602,7 +602,7 @@ again: remove_next = 1 + (end > next->vm_end); if (anon_vma) { VM_BUG_ON(adjust_next && next->anon_vma && anon_vma != next->anon_vma); - anon_vma_lock(anon_vma); + anon_vma_lock_write(anon_vma); anon_vma_interval_tree_pre_update_vma(vma); if (adjust_next) anon_vma_interval_tree_pre_update_vma(next); diff --git a/mm/mremap.c b/mm/mremap.c index 1b61c2d..3dabd17 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -104,7 +104,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, } if (vma->anon_vma) { anon_vma = vma->anon_vma; - anon_vma_lock(anon_vma); + anon_vma_lock_write(anon_vma); } } diff --git a/mm/rmap.c b/mm/rmap.c index 6e3ee3b..b0f612d 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -87,24 +87,24 @@ static inline void anon_vma_free(struct anon_vma *anon_vma) VM_BUG_ON(atomic_read(&anon_vma->refcount)); /* - * Synchronize against page_lock_anon_vma() such that + * Synchronize against page_lock_anon_vma_read() such that * we can safely hold the lock without the anon_vma getting * freed. * * Relies on the full mb implied by the atomic_dec_and_test() from * put_anon_vma() against the acquire barrier implied by - * mutex_trylock() from page_lock_anon_vma(). This orders: + * down_read_trylock() from page_lock_anon_vma_read(). This orders: * - * page_lock_anon_vma() VS put_anon_vma() - * mutex_trylock() atomic_dec_and_test() + * page_lock_anon_vma_read() VS put_anon_vma() + * down_read_trylock() atomic_dec_and_test() * LOCK MB - * atomic_read() mutex_is_locked() + * atomic_read() rwsem_is_locked() * * LOCK should suffice since the actual taking of the lock must * happen _before_ what follows. */ if (rwsem_is_locked(&anon_vma->root->rwsem)) { - anon_vma_lock(anon_vma); + anon_vma_lock_write(anon_vma); anon_vma_unlock(anon_vma); } @@ -146,7 +146,7 @@ static void anon_vma_chain_link(struct vm_area_struct *vma, * allocate a new one. * * Anon-vma allocations are very subtle, because we may have - * optimistically looked up an anon_vma in page_lock_anon_vma() + * optimistically looked up an anon_vma in page_lock_anon_vma_read() * and that may actually touch the spinlock even in the newly * allocated vma (it depends on RCU to make sure that the * anon_vma isn't actually destroyed). @@ -181,7 +181,7 @@ int anon_vma_prepare(struct vm_area_struct *vma) allocated = anon_vma; } - anon_vma_lock(anon_vma); + anon_vma_lock_write(anon_vma); /* page_table_lock to protect against threads */ spin_lock(&mm->page_table_lock); if (likely(!vma->anon_vma)) { @@ -306,7 +306,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) get_anon_vma(anon_vma->root); /* Mark this anon_vma as the one where our new (COWed) pages go. */ vma->anon_vma = anon_vma; - anon_vma_lock(anon_vma); + anon_vma_lock_write(anon_vma); anon_vma_chain_link(vma, avc, anon_vma); anon_vma_unlock(anon_vma); @@ -442,7 +442,7 @@ out: * atomic op -- the trylock. If we fail the trylock, we fall back to getting a * reference like with page_get_anon_vma() and then block on the mutex. */ -struct anon_vma *page_lock_anon_vma(struct page *page) +struct anon_vma *page_lock_anon_vma_read(struct page *page) { struct anon_vma *anon_vma = NULL; struct anon_vma *root_anon_vma; @@ -457,14 +457,14 @@ struct anon_vma *page_lock_anon_vma(struct page *page) anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON); root_anon_vma = ACCESS_ONCE(anon_vma->root); - if (down_write_trylock(&root_anon_vma->rwsem)) { + if (down_read_trylock(&root_anon_vma->rwsem)) { /* * If the page is still mapped, then this anon_vma is still * its anon_vma, and holding the mutex ensures that it will * not go away, see anon_vma_free(). */ if (!page_mapped(page)) { - up_write(&root_anon_vma->rwsem); + up_read(&root_anon_vma->rwsem); anon_vma = NULL; } goto out; @@ -484,15 +484,15 @@ struct anon_vma *page_lock_anon_vma(struct page *page) /* we pinned the anon_vma, its safe to sleep */ rcu_read_unlock(); - anon_vma_lock(anon_vma); + anon_vma_lock_read(anon_vma); if (atomic_dec_and_test(&anon_vma->refcount)) { /* * Oops, we held the last refcount, release the lock * and bail -- can't simply use put_anon_vma() because - * we'll deadlock on the anon_vma_lock() recursion. + * we'll deadlock on the anon_vma_lock_write() recursion. */ - anon_vma_unlock(anon_vma); + anon_vma_unlock_read(anon_vma); __put_anon_vma(anon_vma); anon_vma = NULL; } @@ -504,9 +504,9 @@ out: return anon_vma; } -void page_unlock_anon_vma(struct anon_vma *anon_vma) +void page_unlock_anon_vma_read(struct anon_vma *anon_vma) { - anon_vma_unlock(anon_vma); + anon_vma_unlock_read(anon_vma); } /* @@ -732,7 +732,7 @@ static int page_referenced_anon(struct page *page, struct anon_vma_chain *avc; int referenced = 0; - anon_vma = page_lock_anon_vma(page); + anon_vma = page_lock_anon_vma_read(page); if (!anon_vma) return referenced; @@ -754,7 +754,7 @@ static int page_referenced_anon(struct page *page, break; } - page_unlock_anon_vma(anon_vma); + page_unlock_anon_vma_read(anon_vma); return referenced; } @@ -1474,7 +1474,7 @@ static int try_to_unmap_anon(struct page *page, enum ttu_flags flags) struct anon_vma_chain *avc; int ret = SWAP_AGAIN; - anon_vma = page_lock_anon_vma(page); + anon_vma = page_lock_anon_vma_read(page); if (!anon_vma) return ret; @@ -1501,7 +1501,7 @@ static int try_to_unmap_anon(struct page *page, enum ttu_flags flags) break; } - page_unlock_anon_vma(anon_vma); + page_unlock_anon_vma_read(anon_vma); return ret; } @@ -1696,7 +1696,7 @@ static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *, int ret = SWAP_AGAIN; /* - * Note: remove_migration_ptes() cannot use page_lock_anon_vma() + * Note: remove_migration_ptes() cannot use page_lock_anon_vma_read() * because that depends on page_mapped(); but not all its usages * are holding mmap_sem. Users without mmap_sem are required to * take a reference count to prevent the anon_vma disappearing @@ -1704,7 +1704,7 @@ static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *, anon_vma = page_anon_vma(page); if (!anon_vma) return ret; - anon_vma_lock(anon_vma); + anon_vma_lock_read(anon_vma); anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) { struct vm_area_struct *vma = avc->vma; unsigned long address = vma_address(page, vma); @@ -1712,7 +1712,7 @@ static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *, if (ret != SWAP_AGAIN) break; } - anon_vma_unlock(anon_vma); + anon_vma_unlock_read(anon_vma); return ret; } -- cgit v1.1