[PATCH] io-accounting: write-cancel accounting

Account for the number of byte writes which this process caused to not happen
after all.

Cc: Jay Lan <jlan@sgi.com>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Chris Sturtivant <csturtiv@sgi.com>
Cc: Tony Ernst <tee@sgi.com>
Cc: Guillaume Thouvenin <guillaume.thouvenin@bull.net>
Cc: David Wright <daw@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/buffer.c

@@ -2853,8 +2853,13 @@ int try_to_free_buffers(struct page *page)
 		 * could encounter a non-uptodate page, which is unresolvable.
 		 * This only applies in the rare case where try_to_free_buffers
 		 * succeeds but the page is not freed.
+		 *
+		 * Also, during truncate, discard_buffer will have marked all
+		 * the page's buffers clean.  We discover that here and clean
+		 * the page also.
 		 */
-		clear_page_dirty(page);
+		if (test_clear_page_dirty(page))
+			task_io_account_cancelled_write(PAGE_CACHE_SIZE);
 	}
 out:
 	if (buffers_to_free) {

mm/truncate.c

@@ -13,6 +13,7 @@
 #include <linux/module.h>
 #include <linux/pagemap.h>
 #include <linux/pagevec.h>
+#include <linux/task_io_accounting_ops.h>
 #include <linux/buffer_head.h>	/* grr. try_to_release_page,
 				   do_invalidatepage */
 
@@ -69,7 +70,8 @@ truncate_complete_page(struct address_space *mapping, struct page *page)
 	if (PagePrivate(page))
 		do_invalidatepage(page, 0);
 
-	clear_page_dirty(page);
+	if (test_clear_page_dirty(page))
+		task_io_account_cancelled_write(PAGE_CACHE_SIZE);
 	ClearPageUptodate(page);
 	ClearPageMappedToDisk(page);
 	remove_from_page_cache(page);