Commit 288468c3 authored Aug 09, 2010 by Andrea Arcangeli Committed by Linus Torvalds Aug 09, 2010

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 <aarcange@redhat.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
[kamezawa.hiroyu@jp.fujitsu.com: fix false positive BUG_ON in __page_set_anon_rmap]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent ba6f0ff3

mm/rmap.c

+12 −6

Original line number	Diff line number	Diff line
		@@ -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;

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