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

From: Nick Piggin
Date: Fri Sep 28 2007 - 10:20:39 EST


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@xxxxxxxxxxxx>
> Cc: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
> Cc: Kumar Gala <galak@xxxxxxxxxxxxxxxxxxx>
> Cc: Pete Zaitcev <zaitcev@xxxxxxxxxx>
> Cc: Greg KH <greg@xxxxxxxxx>
> Signed-off-by: Fengguang Wu <wfg@xxxxxxxxxxxxxxxx>
> ---
> 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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