[RFC] mm: change mm_advise_free to clear page dirty

[Wang, Yalin]

This patch add ClearPageDirty() to clear AnonPage dirty flag,
the Anonpage mapcount must be 1, so that this page is only used by
the current process, not shared by other process like fork().
if not clear page dirty for this anon page, the page will never be
treated as freeable.

Signed-off-by: Yalin Wang <yalin.wang@xxxxxxxxxxxxxx>
---
 mm/madvise.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 6d0fcb8..257925a 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -297,22 +297,17 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 			continue;
 
 		page = vm_normal_page(vma, addr, ptent);
-		if (!page)
+		if (!page || !PageAnon(page) || !trylock_page(page))
 			continue;
 
 		if (PageSwapCache(page)) {
-			if (!trylock_page(page))
+			if (!try_to_free_swap(page))
 				continue;
-
-			if (!try_to_free_swap(page)) {
-				unlock_page(page);
-				continue;
-			}
-
-			ClearPageDirty(page);
-			unlock_page(page);
 		}
 
+		if (page_mapcount(page) == 1)
+			ClearPageDirty(page);
+		unlock_page(page);
 		/*
 		 * Some of architecture(ex, PPC) don't update TLB
 		 * with set_pte_at and tlb_remove_tlb_entry so for
-- 
2.2.2
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