PageDirty check in mk_pte for s390

[Martin Schwidefsky <schwidefsky@de.ibm.com>]

Hi Hugh,

I still have the patch below in my patch heap. Should I just go ahead and
add it to my s390-tree or do you prefer to take care of it yourself ?

--
Subject: [PATCH] s390/mm: move PageDirty check from mk_pte to common code

Hugh Dickins commented on the software dirty bit implementation and he
does not like the fact that mk_pte uses PageDirty under the covers.
His suggestion is to move the PageDirty check into the __do_fault
function.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
 arch/s390/include/asm/pgtable.h |  9 +++------
 mm/memory.c                     | 12 ++++++++++++
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 68e6168..d56dc6d 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1260,13 +1260,8 @@ static inline pte_t mk_pte_phys(unsigned long physpage, pgprot_t pgprot)
 static inline pte_t mk_pte(struct page *page, pgprot_t pgprot)
 {
 	unsigned long physpage = page_to_phys(page);
-	pte_t __pte = mk_pte_phys(physpage, pgprot);
 
-	if ((pte_val(__pte) & _PAGE_SWW) && PageDirty(page)) {
-		pte_val(__pte) |= _PAGE_SWC;
-		pte_val(__pte) &= ~_PAGE_RO;
-	}
-	return __pte;
+	return mk_pte_phys(physpage, pgprot);
 }
 
 #define pgd_index(address) (((address) >> PGDIR_SHIFT) & (PTRS_PER_PGD-1))
@@ -1599,6 +1594,8 @@ extern int s390_enable_sie(void);
 static inline void pgtable_cache_init(void) { }
 static inline void check_pgt_cache(void) { }
 
+#define __ARCH_WANT_PTE_WRITE_DIRTY
+
 #include <asm-generic/pgtable.h>
 
 #endif /* _S390_PAGE_H */
diff --git a/mm/memory.c b/mm/memory.c
index 1207cef..765d5f2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3417,6 +3417,18 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 				dirty_page = page;
 				get_page(dirty_page);
 			}
+#ifdef __ARCH_WANT_PTE_WRITE_DIRTY
+			/*
+			 * Architectures that use software dirty bits may
+			 * want to set the dirty bit in the pte if the pte
+			 * is writable and the PageDirty bit is set for the
+			 * page. This avoids unnecessary protection faults
+			 * for writable mappings which do not use
+			 * mapping_cap_account_dirty, e.g. tmpfs and shmem.
+			 */
+			else if (pte_write(entry) && PageDirty(page))
+				entry = pte_mkdirty(entry);
+#endif
 		}
 		set_pte_at(mm, address, page_table, entry);
 
-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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