[PATCH 5/5] vmscan: transfer async file writeback to the flusher

[Wu Fengguang]

This relays all ASYNC file writeback IOs to the flusher threads.
The lesser SYNC pageout()s will work as before (as a last resort).

It's a minimal prototype implementation and barely runs without panic.
It potentially requires lots of more work to go stable. 

Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 mm/vmscan.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- linux-next.orig/mm/vmscan.c	2010-07-29 17:07:07.000000000 +0800
+++ linux-next/mm/vmscan.c	2010-07-29 17:09:16.000000000 +0800
@@ -379,6 +379,13 @@ static pageout_t pageout(struct page *pa
 	}
 	if (mapping->a_ops->writepage == NULL)
 		return PAGE_ACTIVATE;
+
+	if (sync_writeback == PAGEOUT_IO_ASYNC &&
+	    page_is_file_cache(page)) {
+		bdi_start_inode_writeback(mapping->host, page->index);
+		return PAGE_KEEP;
+	}
+
 	if (!may_write_to_queue(mapping->backing_dev_info))
 		return PAGE_KEEP;
 
@@ -1366,7 +1373,6 @@ shrink_inactive_list(unsigned long nr_to
 				list_add(&page->lru, &putback_list);
 			}
 
-			wakeup_flusher_threads(laptop_mode ? 0 : nr_dirty);
 			congestion_wait(BLK_RW_ASYNC, HZ/10);
 
 			/*


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