[PATCH] Remove mapping->vm_writeback

The vm_writeback address_space operation was designed to provide the VM
with a "clustered writeout" capability.  It allowed the filesystem to
perform more intelligent writearound decisions when the VM was trying
to clean a particular page.

I can't say I ever saw any real benefit from this - not much writeout
actually happens on that path - quite a lot of work has gone into
minimising it actually.

The default ->vm_writeback a_op which I provided wrote back the pages
in ->dirty_pages order.  But there is one scenario in which this causes
problems - writing a single 4G file with mem=4G.  We end up with all of
ZONE_NORMAL full of dirty pages, but all writeback effort is against
highmem pages.  (Because there is about 1.5G of dirty memory total).

Net effect: the machine stalls ZONE_NORMAL allocation attempts until
the ->dirty_pages writeback advances onto ZONE_NORMAL pages.

This can be fixed most sweetly with additional radix-tree
infrastructure which will be quite complex.  Later.


So this patch dumps it all, and goes back to using writepage
against individual pages as they come off the LRU.

2 files changed, 0 insertions, 7 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5183f5f7c91c..f39d21e5bcd9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -285,9 +285,6 @@ struct address_space_operations {
 	/* Write back some dirty pages from this mapping. */
 	int (*writepages)(struct address_space *, struct writeback_control *);
 
-	/* Perform a writeback as a memory-freeing operation. */
-	int (*vm_writeback)(struct page *, struct writeback_control *);
-
 	/* Set a page dirty */
 	int (*set_page_dirty)(struct page *page);
 
@@ -1256,9 +1253,6 @@ extern loff_t generic_file_llseek(struct file *file, loff_t offset, int origin);
 extern loff_t remote_llseek(struct file *file, loff_t offset, int origin);
 extern int generic_file_open(struct inode * inode, struct file * filp);
 
-extern int generic_vm_writeback(struct page *page,
-				struct writeback_control *wbc);
-
 static inline void do_generic_file_read(struct file * filp, loff_t *ppos,
 					read_descriptor_t * desc,
 					read_actor_t actor)
diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
index dbfa3ab99699..2a332eed3d82 100644
--- a/include/linux/pagevec.h
+++ b/include/linux/pagevec.h
@@ -21,7 +21,6 @@ void __pagevec_release_nonlru(struct pagevec *pvec);
 void __pagevec_free(struct pagevec *pvec);
 void __pagevec_lru_add(struct pagevec *pvec);
 void __pagevec_lru_add_active(struct pagevec *pvec);
-void pagevec_deactivate_inactive(struct pagevec *pvec);
 void pagevec_strip(struct pagevec *pvec);
 unsigned int pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
 		pgoff_t start, unsigned int nr_pages);