1 files changed, 42 insertions, 28 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 7df7984d476c..cf7e99a87c32 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -56,6 +56,7 @@
 #include <linux/mmu_notifier.h>
 #include <linux/migrate.h>
 #include <linux/hugetlb.h>
+#include <linux/backing-dev.h>
 
 #include <asm/tlbflush.h>
 
@@ -561,6 +562,27 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
 	return address;
 }
 
+pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd = NULL;
+
+	pgd = pgd_offset(mm, address);
+	if (!pgd_present(*pgd))
+		goto out;
+
+	pud = pud_offset(pgd, address);
+	if (!pud_present(*pud))
+		goto out;
+
+	pmd = pmd_offset(pud, address);
+	if (!pmd_present(*pmd))
+		pmd = NULL;
+out:
+	return pmd;
+}
+
 /*
  * Check that @page is mapped at @address into @mm.
  *
@@ -573,8 +595,6 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
 pte_t *__page_check_address(struct page *page, struct mm_struct *mm,
 			  unsigned long address, spinlock_t **ptlp, int sync)
 {
-	pgd_t *pgd;
-	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte;
 	spinlock_t *ptl;
@@ -585,17 +605,10 @@ pte_t *__page_check_address(struct page *page, struct mm_struct *mm,
 		goto check;
 	}
 
-	pgd = pgd_offset(mm, address);
-	if (!pgd_present(*pgd))
+	pmd = mm_find_pmd(mm, address);
+	if (!pmd)
 		return NULL;
 
-	pud = pud_offset(pgd, address);
-	if (!pud_present(*pud))
-		return NULL;
-
-	pmd = pmd_offset(pud, address);
-	if (!pmd_present(*pmd))
-		return NULL;
 	if (pmd_trans_huge(*pmd))
 		return NULL;
 
@@ -926,11 +939,8 @@ int page_mkclean(struct page *page)
 
 	if (page_mapped(page)) {
 		struct address_space *mapping = page_mapping(page);
-		if (mapping) {
+		if (mapping)
 			ret = page_mkclean_file(mapping, page);
-			if (page_test_and_clear_dirty(page_to_pfn(page), 1))
-				ret = 1;
-		}
 	}
 
 	return ret;
@@ -1116,6 +1126,7 @@ void page_add_file_rmap(struct page *page)
  */
 void page_remove_rmap(struct page *page)
 {
+	struct address_space *mapping = page_mapping(page);
 	bool anon = PageAnon(page);
 	bool locked;
 	unsigned long flags;
@@ -1138,8 +1149,21 @@ void page_remove_rmap(struct page *page)
 	 * this if the page is anon, so about to be freed; but perhaps
 	 * not if it's in swapcache - there might be another pte slot
 	 * containing the swap entry, but page not yet written to swap.
+	 *
+	 * And we can skip it on file pages, so long as the filesystem
+	 * participates in dirty tracking (note that this is not only an
+	 * optimization but also solves problems caused by dirty flag in
+	 * storage key getting set by a write from inside kernel); but need to
+	 * catch shm and tmpfs and ramfs pages which have been modified since
+	 * creation by read fault.
+	 *
+	 * Note that mapping must be decided above, before decrementing
+	 * mapcount (which luckily provides a barrier): once page is unmapped,
+	 * it could be truncated and page->mapping reset to NULL at any moment.
+	 * Note also that we are relying on page_mapping(page) to set mapping
+	 * to &swapper_space when PageSwapCache(page).
 	 */
-	if ((!anon || PageSwapCache(page)) &&
+	if (mapping && !mapping_cap_account_dirty(mapping) &&
 	    page_test_and_clear_dirty(page_to_pfn(page), 1))
 		set_page_dirty(page);
 	/*
@@ -1335,8 +1359,6 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
 		struct vm_area_struct *vma, struct page *check_page)
 {
 	struct mm_struct *mm = vma->vm_mm;
-	pgd_t *pgd;
-	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte;
 	pte_t pteval;
@@ -1356,16 +1378,8 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
 	if (end > vma->vm_end)
 		end = vma->vm_end;
 
-	pgd = pgd_offset(mm, address);
-	if (!pgd_present(*pgd))
-		return ret;
-
-	pud = pud_offset(pgd, address);
-	if (!pud_present(*pud))
-		return ret;
-
-	pmd = pmd_offset(pud, address);
-	if (!pmd_present(*pmd))
+	pmd = mm_find_pmd(mm, address);
+	if (!pmd)
 		return ret;
 
 	mmun_start = address;