From: Hugh Dickins Date: Wed, 27 Jun 2007 21:09:53 +0000 (-0700) Subject: mm: kill validate_anon_vma to avoid mapcount BUG X-Git-Tag: v2.6.22-rc7~30 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=30acbabae38793c9c9acace4de5b1c1889570768;p=linux-2.6-omap-h63xx.git mm: kill validate_anon_vma to avoid mapcount BUG validate_anon_vma gave a useful check on the integrity of the anon_vma list when Andrea was developing obj rmap; but it was not enabled in SLES9 itself, nor in mainline, until Nick changed commented-out RMAP_DEBUG to configurable CONFIG_DEBUG_VM in 2.6.17. Now Petr Vandrovec reports that its BUG_ON(mapcount > 100000) can easily crash a CONFIG_DEBUG_VM=y system. That limit was just an arbitrary number to protect against an infinite loop. We could raise it to something enormous (depending on sizeof struct vma and size of memory?); but I rather think validate_anon_vma has outlived its usefulness, and is better just removed - which gives a magnificent performance boost to anything like Petr's test program ;) Of course, a very long anon_vma list is bad news for preemption latency, and I believe there has been one recent report of such: let's not forget that, but validate_anon_vma only makes it worse not better. Signed-off-by: Hugh Dickins Cc: Petr Vandrovec Acked-by: Nick Piggin Cc: Andrea Arcangeli Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/rmap.c b/mm/rmap.c index 850165d32b7..61e492597a0 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -53,24 +53,6 @@ struct kmem_cache *anon_vma_cachep; -static inline void validate_anon_vma(struct vm_area_struct *find_vma) -{ -#ifdef CONFIG_DEBUG_VM - struct anon_vma *anon_vma = find_vma->anon_vma; - struct vm_area_struct *vma; - unsigned int mapcount = 0; - int found = 0; - - list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { - mapcount++; - BUG_ON(mapcount > 100000); - if (vma == find_vma) - found = 1; - } - BUG_ON(!found); -#endif -} - /* This must be called under the mmap_sem. */ int anon_vma_prepare(struct vm_area_struct *vma) { @@ -121,10 +103,8 @@ void __anon_vma_link(struct vm_area_struct *vma) { struct anon_vma *anon_vma = vma->anon_vma; - if (anon_vma) { + if (anon_vma) list_add_tail(&vma->anon_vma_node, &anon_vma->head); - validate_anon_vma(vma); - } } void anon_vma_link(struct vm_area_struct *vma) @@ -134,7 +114,6 @@ void anon_vma_link(struct vm_area_struct *vma) if (anon_vma) { spin_lock(&anon_vma->lock); list_add_tail(&vma->anon_vma_node, &anon_vma->head); - validate_anon_vma(vma); spin_unlock(&anon_vma->lock); } } @@ -148,7 +127,6 @@ void anon_vma_unlink(struct vm_area_struct *vma) return; spin_lock(&anon_vma->lock); - validate_anon_vma(vma); list_del(&vma->anon_vma_node); /* We must garbage collect the anon_vma if it's empty */