linux-kernel - [PATCH] writeback: remove unnecessary wait in throttle_vm

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Message-ID: <20070927015016.GA11080@mail.ustc.edu.cn>
Date:	Thu, 27 Sep 2007 09:50:16 +0800
From:	Fengguang Wu <wfg@...l.ustc.edu.cn>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Kumar Gala <galak@...nel.crashing.org>,
	Pete Zaitcev <zaitcev@...hat.com>, Greg KH <greg@...ah.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] writeback: remove unnecessary wait in
	throttle_vm_writeout()

We don't want to introduce pointless delays in throttle_vm_writeout()
when the writeback limits are not yet exceeded, do we?

Cc: Nick Piggin <nickpiggin@...oo.com.au>
Cc: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc: Kumar Gala <galak@...nel.crashing.org>
Cc: Pete Zaitcev <zaitcev@...hat.com>
Cc: Greg KH <greg@...ah.com>
Signed-off-by: Fengguang Wu <wfg@...l.ustc.edu.cn>
---
 mm/page-writeback.c |   18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

--- linux-2.6.23-rc8-mm1.orig/mm/page-writeback.c
+++ linux-2.6.23-rc8-mm1/mm/page-writeback.c
@@ -507,16 +507,6 @@ void throttle_vm_writeout(gfp_t gfp_mask
 	long background_thresh;
 	long dirty_thresh;
 
-	if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) {
-		/*
-		 * The caller might hold locks which can prevent IO completion
-		 * or progress in the filesystem.  So we cannot just sit here
-		 * waiting for IO to complete.
-		 */
-		congestion_wait(WRITE, HZ/10);
-		return;
-	}
-
         for ( ; ; ) {
 		get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
 
@@ -530,6 +520,14 @@ void throttle_vm_writeout(gfp_t gfp_mask
 			global_page_state(NR_WRITEBACK) <= dirty_thresh)
                         	break;
                 congestion_wait(WRITE, HZ/10);
+
+		/*
+		 * The caller might hold locks which can prevent IO completion
+		 * or progress in the filesystem.  So we cannot just sit here
+		 * waiting for IO to complete.
+		 */
+		if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
+			break;
         }
 }
 

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