[PATCH 4/4] vmscan: transfer async file writeback to the flusher

[Wu Fengguang <fengguang.wu@intel.com>]

[-- Attachment #1: vmscan-writeback-inode-page.patch --]
[-- Type: text/plain, Size: 2241 bytes --]

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.

TODO: avoid OOM if the LRU list is small and/or the storage is slow, so
that the flusher cannot clean enough pages before the LRU is full
scanned.  One simple way could be to do waits on dirty/writeback pages
when priority < 3 for even order 0 allocations.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 mm/page-writeback.c |    2 +-
 mm/vmscan.c         |   13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

--- linux-next.orig/mm/vmscan.c	2010-09-13 19:48:16.000000000 +0800
+++ linux-next/mm/vmscan.c	2010-09-13 20:14:42.000000000 +0800
@@ -756,6 +756,19 @@ static unsigned long shrink_page_list(st
 				}
 			}
 
+			if (page_is_file_cache(page) && mapping &&
+			    sync_writeback == PAGEOUT_IO_ASYNC) {
+				if (!bdi_start_inode_writeback(
+					mapping->backing_dev_info,
+					mapping->host, page_index(page))) {
+					SetPageReclaim(page);
+					goto keep_locked;
+				} else if (!current_is_kswapd() &&
+					   printk_ratelimit()) {
+					printk(KERN_INFO "cannot pageout\n");
+				}
+			}
+
 			if (references == PAGEREF_RECLAIM_CLEAN)
 				goto keep_locked;
 			if (!may_enter_fs)
--- linux-next.orig/mm/page-writeback.c	2010-09-13 19:48:16.000000000 +0800
+++ linux-next/mm/page-writeback.c	2010-09-13 20:06:26.000000000 +0800
@@ -1232,6 +1232,7 @@ int set_page_dirty(struct page *page)
 {
 	struct address_space *mapping = page_mapping(page);
 
+	ClearPageReclaim(page);
 	if (likely(mapping)) {
 		int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
 #ifdef CONFIG_BLOCK
@@ -1289,7 +1290,6 @@ int clear_page_dirty_for_io(struct page 
 
 	BUG_ON(!PageLocked(page));
 
-	ClearPageReclaim(page);
 	if (mapping && mapping_cap_account_dirty(mapping)) {
 		/*
 		 * Yes, Virginia, this is indeed insane.


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