From 288468c334e98aacbb7e2fb8bde6bc1adcd55e05 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Mon, 9 Aug 2010 17:19:09 -0700 Subject: [PATCH] rmap: always use anon_vma root pointer Always use anon_vma->root pointer instead of anon_vma_chain.prev. Also optimize the map-paths, if a mapping is already established no need to overwrite it with root anon-vma list, we can keep the more finegrined anon-vma and skip the overwrite: see the PageAnon check in !exclusive case. This is also the optimization that hidden the ksm bug as this tends to make ksm_might_need_to_copy skip the copy, but only the proper fix to ksm_might_need_to_copy guarantees not triggering the ksm bug unless ksm is in use. this is an optimization only... [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Andrea Arcangeli Signed-off-by: Rik van Riel [kamezawa.hiroyu@jp.fujitsu.com: fix false positive BUG_ON in __page_set_anon_rmap] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/rmap.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index dce74a9efdd..f5d6799b8a7 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -767,14 +767,20 @@ static void __page_set_anon_rmap(struct page *page, * If the page isn't exclusively mapped into this vma, * we must use the _oldest_ possible anon_vma for the * page mapping! - * - * So take the last AVC chain entry in the vma, which is - * the deepest ancestor, and use the anon_vma from that. */ if (!exclusive) { - struct anon_vma_chain *avc; - avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma); - anon_vma = avc->anon_vma; + if (PageAnon(page)) + return; + anon_vma = anon_vma->root; + } else { + /* + * In this case, swapped-out-but-not-discarded swap-cache + * is remapped. So, no need to update page->mapping here. + * We convice anon_vma poitned by page->mapping is not obsolete + * because vma->anon_vma is necessary to be a family of it. + */ + if (PageAnon(page)) + return; } anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; -- 2.20.1