[PATCH] io-accounting: write accounting

Accounting writes is fairly simple: whenever a process flips a page from clean
to dirty, we accuse it of having caused a write to underlying storage of
PAGE_CACHE_SIZE bytes.

This may overestimate the amount of writing: the page-dirtying may cause only
one buffer_head's worth of writeout.  Fixing that is possible, but probably a
bit messy and isn't obviously important.

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: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/buffer.c

@@ -35,6 +35,7 @@
 #include <linux/hash.h>
 #include <linux/suspend.h>
 #include <linux/buffer_head.h>
+#include <linux/task_io_accounting_ops.h>
 #include <linux/bio.h>
 #include <linux/notifier.h>
 #include <linux/cpu.h>
@@ -729,8 +730,10 @@ int __set_page_dirty_buffers(struct page *page)
 
 	write_lock_irq(&mapping->tree_lock);
 	if (page->mapping) {	/* Race with truncate? */
-		if (mapping_cap_account_dirty(mapping))
+		if (mapping_cap_account_dirty(mapping)) {
 			__inc_zone_page_state(page, NR_FILE_DIRTY);
+			task_io_account_write(PAGE_CACHE_SIZE);
+		}
 		radix_tree_tag_set(&mapping->page_tree,
 				page_index(page), PAGECACHE_TAG_DIRTY);
 	}

mm/page-writeback.c

@@ -21,6 +21,7 @@
 #include <linux/writeback.h>
 #include <linux/init.h>
 #include <linux/backing-dev.h>
+#include <linux/task_io_accounting_ops.h>
 #include <linux/blkdev.h>
 #include <linux/mpage.h>
 #include <linux/rmap.h>
@@ -768,8 +769,10 @@ int __set_page_dirty_nobuffers(struct page *page)
 		mapping2 = page_mapping(page);
 		if (mapping2) { /* Race with truncate? */
 			BUG_ON(mapping2 != mapping);
-			if (mapping_cap_account_dirty(mapping))
+			if (mapping_cap_account_dirty(mapping)) {
 				__inc_zone_page_state(page, NR_FILE_DIRTY);
+				task_io_account_write(PAGE_CACHE_SIZE);
+			}
 			radix_tree_tag_set(&mapping->page_tree,
 				page_index(page), PAGECACHE_TAG_DIRTY);
 		}