linux-kernel - Re: [PATCH 18/35] writeback: start background writeback earlier

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 16 Dec 2010 13:37:57 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Dave Chinner <david@...morbit.com>,
	Theodore Ts'o <tytso@....edu>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Greg Thelen <gthelen@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	linux-mm <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 18/35] writeback: start background writeback earlier

On Mon, Dec 13, 2010 at 10:47:04PM +0800, Wu, Fengguang wrote:
> It's possible for some one to suddenly eat lots of memory,
> leading to sudden drop of global dirty limit. So a dirtier
> task may get hard throttled immediately without some previous
> balance_dirty_pages() call to invoke background writeback.
> 
> In this case we need to check for background writeback earlier in the
> loop to avoid stucking the application for very long time. This was not
> a problem before the IO-less balance_dirty_pages() because it will try
> to write something and then break out of the loop regardless of the
> global limit.
> 
> Another scheme this check will help is, the dirty limit is too close to
> the background threshold, so that someone manages to jump directly into
> the pause threshold (background+dirty)/2.
> 
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
>  mm/page-writeback.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> --- linux-next.orig/mm/page-writeback.c	2010-12-13 21:46:16.000000000 +0800
> +++ linux-next/mm/page-writeback.c	2010-12-13 21:46:17.000000000 +0800
> @@ -748,6 +748,9 @@ static void balance_dirty_pages(struct a
>  				    bdi_stat(bdi, BDI_WRITEBACK);
>  		}
>  
> +		if (unlikely(!writeback_in_progress(bdi)))
> +			bdi_start_background_writeback(bdi);
> +
>  		bdi_update_bandwidth(bdi, start_time, bdi_dirty, bdi_thresh);
>  
>  		/*
> 

The above patch allows this simplification.
---
Subject: writeback: start background writeback earlier - handle laptop mode
Date: Wed Dec 15 20:15:54 CST 2010

The laptop mode handling can be simplified since we've kick background
writeback inside the balance_dirty_pages() loop on dirty_exceeded.

Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
---
 mm/page-writeback.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- linux-next.orig/mm/page-writeback.c	2010-12-15 20:14:33.000000000 +0800
+++ linux-next/mm/page-writeback.c	2010-12-15 20:15:39.000000000 +0800
@@ -891,8 +891,10 @@ pause:
 	 * In normal mode, we start background writeout at the lower
 	 * background_thresh, to keep the amount of dirty memory low.
 	 */
-	if ((laptop_mode && dirty_exceeded) ||
-	    (!laptop_mode && (nr_reclaimable > background_thresh)))
+	if (laptop_mode)
+		return;
+
+	if (nr_reclaimable > background_thresh)
 		bdi_start_background_writeback(bdi);
 }
 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/