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@xxxxxxxxxx>
---
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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