linux-kernel - Re: [PATCH v2 2/3] move ClearPageReclaim

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Date:	Mon, 29 Nov 2010 15:29:51 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ben Gamari <bgamari.foss@...il.com>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...nel.dk>, Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH v2 2/3] move ClearPageReclaim

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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