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Subject[PATCHv4 35/39] mm: decomposite do_wp_page() and get rid of some 'goto' logic
Date
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

Let's extract some 'reuse' path to separate function and use it instead
of ugly goto.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
mm/memory.c | 110 ++++++++++++++++++++++++++++++++---------------------------
1 file changed, 59 insertions(+), 51 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 8997cd8..eb99ab1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2594,6 +2594,52 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo
copy_user_highpage(dst, src, va, vma);
}

+static void dirty_page(struct vm_area_struct *vma, struct page *page,
+ bool page_mkwrite)
+{
+ /*
+ * Yes, Virginia, this is actually required to prevent a race
+ * with clear_page_dirty_for_io() from clearing the page dirty
+ * bit after it clear all dirty ptes, but before a racing
+ * do_wp_page installs a dirty pte.
+ *
+ * __do_fault is protected similarly.
+ */
+ if (!page_mkwrite) {
+ wait_on_page_locked(page);
+ set_page_dirty_balance(page, page_mkwrite);
+ /* file_update_time outside page_lock */
+ if (vma->vm_file)
+ file_update_time(vma->vm_file);
+ }
+ put_page(page);
+ if (page_mkwrite) {
+ struct address_space *mapping = page->mapping;
+
+ set_page_dirty(page);
+ unlock_page(page);
+ page_cache_release(page);
+ if (mapping) {
+ /*
+ * Some device drivers do not set page.mapping
+ * but still dirty their pages
+ */
+ balance_dirty_pages_ratelimited(mapping);
+ }
+ }
+}
+
+static void mkwrite_pte(struct vm_area_struct *vma, unsigned long address,
+ pte_t *page_table, pte_t orig_pte)
+{
+ pte_t entry;
+ flush_cache_page(vma, address, pte_pfn(orig_pte));
+ entry = pte_mkyoung(orig_pte);
+ entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+ if (ptep_set_access_flags(vma, address, page_table, entry, 1))
+ update_mmu_cache(vma, address, page_table);
+}
+
/*
* This routine handles present pages, when users try to write
* to a shared page. It is done by copying the page to a new address
@@ -2618,10 +2664,8 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
__releases(ptl)
{
struct page *old_page, *new_page = NULL;
- pte_t entry;
int ret = 0;
int page_mkwrite = 0;
- struct page *dirty_page = NULL;
unsigned long mmun_start = 0; /* For mmu_notifiers */
unsigned long mmun_end = 0; /* For mmu_notifiers */

@@ -2635,8 +2679,11 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
* accounting on raw pfn maps.
*/
if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
- (VM_WRITE|VM_SHARED))
- goto reuse;
+ (VM_WRITE|VM_SHARED)) {
+ mkwrite_pte(vma, address, page_table, orig_pte);
+ pte_unmap_unlock(page_table, ptl);
+ return VM_FAULT_WRITE;
+ }
goto gotten;
}

@@ -2665,7 +2712,9 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
*/
page_move_anon_rmap(old_page, vma, address);
unlock_page(old_page);
- goto reuse;
+ mkwrite_pte(vma, address, page_table, orig_pte);
+ pte_unmap_unlock(page_table, ptl);
+ return VM_FAULT_WRITE;
}
unlock_page(old_page);
} else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
@@ -2727,53 +2776,11 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,

page_mkwrite = 1;
}
- dirty_page = old_page;
- get_page(dirty_page);
-
-reuse:
- flush_cache_page(vma, address, pte_pfn(orig_pte));
- entry = pte_mkyoung(orig_pte);
- entry = maybe_mkwrite(pte_mkdirty(entry), vma);
- if (ptep_set_access_flags(vma, address, page_table, entry,1))
- update_mmu_cache(vma, address, page_table);
+ get_page(old_page);
+ mkwrite_pte(vma, address, page_table, orig_pte);
pte_unmap_unlock(page_table, ptl);
- ret |= VM_FAULT_WRITE;
-
- if (!dirty_page)
- return ret;
-
- /*
- * Yes, Virginia, this is actually required to prevent a race
- * with clear_page_dirty_for_io() from clearing the page dirty
- * bit after it clear all dirty ptes, but before a racing
- * do_wp_page installs a dirty pte.
- *
- * __do_fault is protected similarly.
- */
- if (!page_mkwrite) {
- wait_on_page_locked(dirty_page);
- set_page_dirty_balance(dirty_page, page_mkwrite);
- /* file_update_time outside page_lock */
- if (vma->vm_file)
- file_update_time(vma->vm_file);
- }
- put_page(dirty_page);
- if (page_mkwrite) {
- struct address_space *mapping = dirty_page->mapping;
-
- set_page_dirty(dirty_page);
- unlock_page(dirty_page);
- page_cache_release(dirty_page);
- if (mapping) {
- /*
- * Some device drivers do not set page.mapping
- * but still dirty their pages
- */
- balance_dirty_pages_ratelimited(mapping);
- }
- }
-
- return ret;
+ dirty_page(vma, old_page, page_mkwrite);
+ return ret | VM_FAULT_WRITE;
}

/*
@@ -2810,6 +2817,7 @@ gotten:
*/
page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
if (likely(pte_same(*page_table, orig_pte))) {
+ pte_t entry;
if (old_page) {
if (!PageAnon(old_page)) {
dec_mm_counter_fast(mm, MM_FILEPAGES);
--
1.7.10.4


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