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

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Message-Id: <200709280749.09822.nickpiggin@yahoo.com.au>
Date:	Fri, 28 Sep 2007 07:49:09 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Fengguang Wu <wfg@...l.ustc.edu.cn>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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: Re: [PATCH] writeback: remove unnecessary wait in throttle_vm_writeout()

On Thursday 27 September 2007 11:50, Fengguang Wu wrote:
> We don't want to introduce pointless delays in throttle_vm_writeout()
> when the writeback limits are not yet exceeded, do we?

I don't think so (ie. I agree with you).
IIRC, Marcelo initially did the throttle_vm_writeout?

> 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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