mm: set_page_dirty_balance() vs ->page_mkwrite()

All the current page_mkwrite() implementations also set the page dirty. Which
results in the set_page_dirty_balance() call to _not_ call balance, because the
page is already found dirty.

This allows us to dirty a _lot_ of pages without ever hitting
balance_dirty_pages().  Not good (tm).

Force a balance call if ->page_mkwrite() was successful.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 10 insertions, 5 deletions

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 4ef4d22e5e43..b4af6bcb7b7a 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -127,7 +127,7 @@ int sync_page_range(struct inode *inode, struct address_space *mapping,
                         loff_t pos, loff_t count);
 int sync_page_range_nolock(struct inode *inode, struct address_space *mapping,
                            loff_t pos, loff_t count);
-void set_page_dirty_balance(struct page *page);
+void set_page_dirty_balance(struct page *page, int page_mkwrite);
 void writeback_set_ratelimit(void);
 
 /* pdflush.c */
diff --git a/mm/memory.c b/mm/memory.c
index c0e7741a98de..f82b359b2745 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1639,6 +1639,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
         struct page *old_page, *new_page;
         pte_t entry;
         int reuse = 0, ret = 0;
+        int page_mkwrite = 0;
         struct page *dirty_page = NULL;
 
         old_page = vm_normal_page(vma, address, orig_pte);
@@ -1687,6 +1688,8 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
                         page_cache_release(old_page);
                         if (!pte_same(*page_table, orig_pte))
                                 goto unlock;
+
+                        page_mkwrite = 1;
                 }
                 dirty_page = old_page;
                 get_page(dirty_page);
@@ -1774,7 +1777,7 @@ unlock:
                  * do_no_page is protected similarly.
                  */
                 wait_on_page_locked(dirty_page);
-                set_page_dirty_balance(dirty_page);
+                set_page_dirty_balance(dirty_page, page_mkwrite);
                 put_page(dirty_page);
         }
         return ret;
@@ -2322,6 +2325,7 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
         struct page *dirty_page = NULL;
         struct vm_fault vmf;
         int ret;
+        int page_mkwrite = 0;
 
         vmf.virtual_address = (void __user *)(address & PAGE_MASK);
         vmf.pgoff = pgoff;
@@ -2398,6 +2402,7 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                                         anon = 1; /* no anon but release vmf.page */
                                         goto out;
                                 }
+                                page_mkwrite = 1;
                         }
                 }
 
@@ -2453,7 +2458,7 @@ out_unlocked:
         if (anon)
                 page_cache_release(vmf.page);
         else if (dirty_page) {
-                set_page_dirty_balance(dirty_page);
+                set_page_dirty_balance(dirty_page, page_mkwrite);
                 put_page(dirty_page);
         }
 
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 63512a9ed57e..44720363374c 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -274,9 +274,9 @@ static void balance_dirty_pages(struct address_space *mapping)
                 pdflush_operation(background_writeout, 0);
 }
 
-void set_page_dirty_balance(struct page *page)
+void set_page_dirty_balance(struct page *page, int page_mkwrite)
 {
-        if (set_page_dirty(page)) {
+        if (set_page_dirty(page) || page_mkwrite) {
                 struct address_space *mapping = page_mapping(page);
 
                 if (mapping)