[PATCH 02/38] mm: drop support of non-linear mapping from fault codepath

Kirill A. Shutemov
2014-12-24T12:23:33Z

We don't create non-linear mappings anymore. Let's drop code which
handles them on page fault.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
include/linux/mm.h | 16 ++++++--------
mm/memory.c | 65 ++++++++----------------------------------------------
2 files changed, 16 insertions(+), 65 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 07574d8072f4..7c7761536f5f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -206,21 +206,19 @@ extern unsigned int kobjsize(const void *objp);
extern pgprot_t protection_map[16];

#define FAULT_FLAG_WRITE 0x01 /* Fault was a write access */
-#define FAULT_FLAG_NONLINEAR 0x02 /* Fault was via a nonlinear mapping */
-#define FAULT_FLAG_MKWRITE 0x04 /* Fault was mkwrite of existing pte */
-#define FAULT_FLAG_ALLOW_RETRY 0x08 /* Retry fault if blocking */
-#define FAULT_FLAG_RETRY_NOWAIT 0x10 /* Don't drop mmap_sem and wait when retrying */
-#define FAULT_FLAG_KILLABLE 0x20 /* The fault task is in SIGKILL killable region */
-#define FAULT_FLAG_TRIED 0x40 /* second try */
-#define FAULT_FLAG_USER 0x80 /* The fault originated in userspace */
+#define FAULT_FLAG_MKWRITE 0x02 /* Fault was mkwrite of existing pte */
+#define FAULT_FLAG_ALLOW_RETRY 0x04 /* Retry fault if blocking */
+#define FAULT_FLAG_RETRY_NOWAIT 0x08 /* Don't drop mmap_sem and wait when retrying */
+#define FAULT_FLAG_KILLABLE 0x10 /* The fault task is in SIGKILL killable region */
+#define FAULT_FLAG_TRIED 0x20 /* Second try */
+#define FAULT_FLAG_USER 0x40 /* The fault originated in userspace */

/*
* vm_fault is filled by the the pagefault handler and passed to the vma's
* ->fault function. The vma's ->fault is responsible for returning a bitmask
* of VM_FAULT_xxx flags that give details about how the fault was handled.
*
- * pgoff should be used in favour of virtual_address, if possible. If pgoff
- * is used, one may implement ->remap_pages to get nonlinear mapping support.
+ * pgoff should be used in favour of virtual_address, if possible.
*/
struct vm_fault {
unsigned int flags; /* FAULT_FLAG_xxx flags */
diff --git a/mm/memory.c b/mm/memory.c
index 5216b91a714a..587522630b10 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1899,12 +1899,11 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
EXPORT_SYMBOL_GPL(apply_to_page_range);

/*
- * handle_pte_fault chooses page fault handler according to an entry
- * which was read non-atomically. Before making any commitment, on
- * those architectures or configurations (e.g. i386 with PAE) which
- * might give a mix of unmatched parts, do_swap_page and do_nonlinear_fault
- * must check under lock before unmapping the pte and proceeding
- * (but do_wp_page is only called after already making such a check;
+ * handle_pte_fault chooses page fault handler according to an entry which was
+ * read non-atomically. Before making any commitment, on those architectures
+ * or configurations (e.g. i386 with PAE) which might give a mix of unmatched
+ * parts, do_swap_page must check under lock before unmapping the pte and
+ * proceeding (but do_wp_page is only called after already making such a check;
* and do_anonymous_page can safely check later on).
*/
static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
@@ -2703,8 +2702,6 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address,
entry = mk_pte(page, vma->vm_page_prot);
if (write)
entry = maybe_mkwrite(pte_mkdirty(entry), vma);
- else if (pte_file(*pte) && pte_file_soft_dirty(*pte))
- entry = pte_mksoft_dirty(entry);
if (anon) {
inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
page_add_new_anon_rmap(page, vma, address);
@@ -2839,8 +2836,7 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma,
* if page by the offset is not ready to be mapped (cold cache or
* something).
*/
- if (vma->vm_ops->map_pages && !(flags & FAULT_FLAG_NONLINEAR) &&
- fault_around_bytes >> PAGE_SHIFT > 1) {
+ if (vma->vm_ops->map_pages && fault_around_bytes >> PAGE_SHIFT > 1) {
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
do_fault_around(vma, address, pte, pgoff, flags);
if (!pte_same(*pte, orig_pte))
@@ -2987,7 +2983,7 @@ static int do_shared_fault(struct mm_struct *mm, struct vm_area_struct *vma,
* The mmap_sem may have been released depending on flags and our
* return value. See filemap_fault() and __lock_page_or_retry().
*/
-static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
+static int do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long address, pte_t *page_table, pmd_t *pmd,
unsigned int flags, pte_t orig_pte)
{
@@ -3004,46 +3000,6 @@ static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
return do_shared_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
}

-/*
- * Fault of a previously existing named mapping. Repopulate the pte
- * from the encoded file_pte if possible. This enables swappable
- * nonlinear vmas.
- *
- * We enter with non-exclusive mmap_sem (to exclude vma changes,
- * but allow concurrent faults), and pte mapped but not yet locked.
- * We return with pte unmapped and unlocked.
- * The mmap_sem may have been released depending on flags and our
- * return value. See filemap_fault() and __lock_page_or_retry().
- */
-static int do_nonlinear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
- unsigned long address, pte_t *page_table, pmd_t *pmd,
- unsigned int flags, pte_t orig_pte)
-{
- pgoff_t pgoff;
-
- flags |= FAULT_FLAG_NONLINEAR;
-
- if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
- return 0;
-
- if (unlikely(!(vma->vm_flags & VM_NONLINEAR))) {
- /*
- * Page table corrupted: show pte and kill process.
- */
- print_bad_pte(vma, address, orig_pte, NULL);
- return VM_FAULT_SIGBUS;
- }
-
- pgoff = pte_to_pgoff(orig_pte);
- if (!(flags & FAULT_FLAG_WRITE))
- return do_read_fault(mm, vma, address, pmd, pgoff, flags,
- orig_pte);
- if (!(vma->vm_flags & VM_SHARED))
- return do_cow_fault(mm, vma, address, pmd, pgoff, flags,
- orig_pte);
- return do_shared_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
-}
-
static int numa_migrate_prep(struct page *page, struct vm_area_struct *vma,
unsigned long addr, int page_nid,
int *flags)
@@ -3171,15 +3127,12 @@ static int handle_pte_fault(struct mm_struct *mm,
if (pte_none(entry)) {
if (vma->vm_ops) {
if (likely(vma->vm_ops->fault))
- return do_linear_fault(mm, vma, address,
- pte, pmd, flags, entry);
+ return do_fault(mm, vma, address, pte,
+ pmd, flags, entry);
}
return do_anonymous_page(mm, vma, address,
pte, pmd, flags);
}
- if (pte_file(entry))
- return do_nonlinear_fault(mm, vma, address,
- pte, pmd, flags, entry);
return do_swap_page(mm, vma, address,
pte, pmd, flags, entry);
}
--
2.1.3