Re: [PATCH] writeback: remove unnecessary wait in throttle_vm_writeout()

[Nick Piggin <nickpiggin@yahoo.com.au>]

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@yahoo.com.au>
> Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
> Cc: Kumar Gala <galak@kernel.crashing.org>
> Cc: Pete Zaitcev <zaitcev@redhat.com>
> Cc: Greg KH <greg@kroah.com>
> Signed-off-by: Fengguang Wu <wfg@mail.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;
>          }
>  }