Re: [PATCH v2 2/3] move ClearPageReclaim

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

On Sun, Nov 28, 2010 at 11:02:56PM +0800, Minchan Kim wrote:
> fe3cba17 added ClearPageReclaim into clear_page_dirty_for_io for
> preventing fast reclaiming readahead marker page.
> 
> In this series, PG_reclaim is used by invalidated page, too.
> If VM find the page is invalidated and it's dirty, it sets PG_reclaim
> to reclaim asap. Then, when the dirty page will be writeback,
> clear_page_dirty_for_io will clear PG_reclaim unconditionally.
> It disturbs this serie's goal.
> 
> I think it's okay to clear PG_readahead when the page is dirty, not
> writeback time. So this patch moves ClearPageReadahead.
> This patch needs Wu's opinion.

It's a safe change. The possibility and consequence of races are both
small enough. However the patch could be simplified as follows?

Thanks,
Fengguang
---

--- linux-next.orig/mm/page-writeback.c	2010-11-29 15:14:54.000000000 +0800
+++ linux-next/mm/page-writeback.c	2010-11-29 15:15:02.000000000 +0800
@@ -1330,6 +1330,7 @@ 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
@@ -1387,7 +1388,6 @@ 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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