linux-kernel - [PATCH][-mm] remove redundant page->mapping check

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Message-Id: <20080618164349.37B6.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Wed, 18 Jun 2008 16:54:01 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com, Rik van Riel <riel@...hat.com>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org
Subject: [PATCH][-mm] remove redundant page->mapping check

> > > this part is really necessary?
> > > I tryed to remove it, but any problem doesn't happend.
> > > 
> > I made this part first, and added a fix for migration_entry_wait later.
> > 
> > So, I haven't test without this part, and I think it will cause
> > VM_BUG_ON() here without this part.
> > 
> > Anyway, I will test it.
> > 
> I got this VM_BUG_ON() as expected only by doing:
> 
>   # echo $$ >/cgroup/cpuset/02/tasks
> 
> So, I beleive that both fixes for migration_entry_wait and
> unmap_and_move (and, of course, removal VM_BUG_ON from
> putback_lru_page) are needed.

OK, I confirmed this part.

Andrew, please pick.


==================================================

Against: 2.6.26-rc5-mm3

remove redundant mapping check.

we'd be doing exactly what putback_lru_page() is doing.  So, this code
as always unnecessary, duplicate code.
So, just let putback_lru_page() handle this condition and conditionally
unlock_page().


Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Acked-by:      Lee Schermerhorn <Lee.Schermerhorn@...com>

---
 mm/migrate.c |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

Index: b/mm/migrate.c
===================================================================
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -716,13 +716,7 @@ unlock:
  		 * restored.
  		 */
  		list_del(&page->lru);
-		if (!page->mapping) {
-			VM_BUG_ON(page_count(page) != 1);
-			unlock_page(page);
-			put_page(page);		/* just free the old page */
-			goto end_migration;
-		} else
-			unlock = putback_lru_page(page);
+		unlock = putback_lru_page(page);
 	}
 
 	if (unlock)



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