* [PATCH 10/13] writeback: make reasonable gap between the dirty/background thresholds
@ 2010-11-17 3:58 Wu Fengguang
0 siblings, 0 replies; 4+ messages in thread
From: Wu Fengguang @ 2010-11-17 3:58 UTC (permalink / raw)
To: Andrew Morton
Cc: Theodore Ts'o, Wu Fengguang, Dave Chinner, Jan Kara,
Peter Zijlstra, Mel Gorman, Rik van Riel, KOSAKI Motohiro,
Chris Mason, Christoph Hellwig, linux-mm, linux-fsdevel, LKML
Andrew,
References: <20101117035821.000579293@intel.com>
Content-Disposition: inline; filename=writeback-fix-oversize-background-thresh.patch
The change is virtually a no-op for the majority users that use the
default 10/20 background/dirty ratios. For others don't know why they
are setting background ratio close enough to dirty ratio. Someone must
set background ratio equal to dirty ratio, but no one seems to notice or
complain that it's then silently halved under the hood..
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
mm/page-writeback.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- linux-next.orig/mm/page-writeback.c 2010-11-15 13:12:50.000000000 +0800
+++ linux-next/mm/page-writeback.c 2010-11-15 13:13:42.000000000 +0800
@@ -403,8 +403,15 @@ void global_dirty_limits(unsigned long *
else
background = (dirty_background_ratio * available_memory) / 100;
- if (background >= dirty)
- background = dirty / 2;
+ /*
+ * Ensure at least 1/4 gap between background and dirty thresholds, so
+ * that when dirty throttling starts at (background + dirty)/2, it's at
+ * the entrance of bdi soft throttle threshold, so as to avoid being
+ * hard throttled.
+ */
+ if (background > dirty - dirty * 2 / BDI_SOFT_DIRTY_LIMIT)
+ background = dirty - dirty * 2 / BDI_SOFT_DIRTY_LIMIT;
+
tsk = current;
if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
background += background / 4;
--
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^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH 10/13] writeback: make reasonable gap between the dirty/background thresholds
2010-11-17 4:27 [PATCH 00/13] IO-less dirty throttling v2 Wu Fengguang
@ 2010-11-17 4:27 ` Wu Fengguang
2010-11-24 11:18 ` Peter Zijlstra
0 siblings, 1 reply; 4+ messages in thread
From: Wu Fengguang @ 2010-11-17 4:27 UTC (permalink / raw)
To: Andrew Morton
Cc: Jan Kara, Wu Fengguang, Christoph Hellwig, Dave Chinner,
Theodore Ts'o, Chris Mason, Peter Zijlstra, Mel Gorman,
Rik van Riel, KOSAKI Motohiro, linux-mm, linux-fsdevel, LKML
[-- Attachment #1: writeback-fix-oversize-background-thresh.patch --]
[-- Type: text/plain, Size: 1600 bytes --]
The change is virtually a no-op for the majority users that use the
default 10/20 background/dirty ratios. For others don't know why they
are setting background ratio close enough to dirty ratio. Someone must
set background ratio equal to dirty ratio, but no one seems to notice or
complain that it's then silently halved under the hood..
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
mm/page-writeback.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- linux-next.orig/mm/page-writeback.c 2010-11-15 13:12:50.000000000 +0800
+++ linux-next/mm/page-writeback.c 2010-11-15 13:13:42.000000000 +0800
@@ -403,8 +403,15 @@ void global_dirty_limits(unsigned long *
else
background = (dirty_background_ratio * available_memory) / 100;
- if (background >= dirty)
- background = dirty / 2;
+ /*
+ * Ensure at least 1/4 gap between background and dirty thresholds, so
+ * that when dirty throttling starts at (background + dirty)/2, it's at
+ * the entrance of bdi soft throttle threshold, so as to avoid being
+ * hard throttled.
+ */
+ if (background > dirty - dirty * 2 / BDI_SOFT_DIRTY_LIMIT)
+ background = dirty - dirty * 2 / BDI_SOFT_DIRTY_LIMIT;
+
tsk = current;
if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
background += background / 4;
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 10/13] writeback: make reasonable gap between the dirty/background thresholds
2010-11-17 4:27 ` [PATCH 10/13] writeback: make reasonable gap between the dirty/background thresholds Wu Fengguang
@ 2010-11-24 11:18 ` Peter Zijlstra
2010-11-24 12:48 ` Wu Fengguang
0 siblings, 1 reply; 4+ messages in thread
From: Peter Zijlstra @ 2010-11-24 11:18 UTC (permalink / raw)
To: Wu Fengguang
Cc: Andrew Morton, Jan Kara, Christoph Hellwig, Dave Chinner,
Theodore Ts'o, Chris Mason, Mel Gorman, Rik van Riel,
KOSAKI Motohiro, linux-mm, linux-fsdevel, LKML
On Wed, 2010-11-17 at 12:27 +0800, Wu Fengguang wrote:
> plain text document attachment
> (writeback-fix-oversize-background-thresh.patch)
> The change is virtually a no-op for the majority users that use the
> default 10/20 background/dirty ratios. For others don't know why they
> are setting background ratio close enough to dirty ratio. Someone must
> set background ratio equal to dirty ratio, but no one seems to notice or
> complain that it's then silently halved under the hood..
>
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
> mm/page-writeback.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> --- linux-next.orig/mm/page-writeback.c 2010-11-15 13:12:50.000000000 +0800
> +++ linux-next/mm/page-writeback.c 2010-11-15 13:13:42.000000000 +0800
> @@ -403,8 +403,15 @@ void global_dirty_limits(unsigned long *
> else
> background = (dirty_background_ratio * available_memory) / 100;
>
> - if (background >= dirty)
> - background = dirty / 2;
> + /*
> + * Ensure at least 1/4 gap between background and dirty thresholds, so
> + * that when dirty throttling starts at (background + dirty)/2, it's at
> + * the entrance of bdi soft throttle threshold, so as to avoid being
> + * hard throttled.
> + */
> + if (background > dirty - dirty * 2 / BDI_SOFT_DIRTY_LIMIT)
> + background = dirty - dirty * 2 / BDI_SOFT_DIRTY_LIMIT;
> +
> tsk = current;
> if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
> background += background / 4;
Hrm,.. the alternative is to return -ERANGE or somesuch when people try
to write nonsensical values.
I'm not sure what's best, guessing at what the user did mean to do or
forcing him to actually think.
--
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 10/13] writeback: make reasonable gap between the dirty/background thresholds
2010-11-24 11:18 ` Peter Zijlstra
@ 2010-11-24 12:48 ` Wu Fengguang
0 siblings, 0 replies; 4+ messages in thread
From: Wu Fengguang @ 2010-11-24 12:48 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Andrew Morton, Jan Kara, Christoph Hellwig, Dave Chinner,
Theodore Ts'o, Chris Mason, Mel Gorman, Rik van Riel,
KOSAKI Motohiro, linux-mm, linux-fsdevel@vger.kernel.org, LKML
On Wed, Nov 24, 2010 at 07:18:18PM +0800, Peter Zijlstra wrote:
> On Wed, 2010-11-17 at 12:27 +0800, Wu Fengguang wrote:
> > plain text document attachment
> > (writeback-fix-oversize-background-thresh.patch)
> > The change is virtually a no-op for the majority users that use the
> > default 10/20 background/dirty ratios. For others don't know why they
> > are setting background ratio close enough to dirty ratio. Someone must
> > set background ratio equal to dirty ratio, but no one seems to notice or
> > complain that it's then silently halved under the hood..
> >
> > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> > ---
> > mm/page-writeback.c | 11 +++++++++--
> > 1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > --- linux-next.orig/mm/page-writeback.c 2010-11-15 13:12:50.000000000 +0800
> > +++ linux-next/mm/page-writeback.c 2010-11-15 13:13:42.000000000 +0800
> > @@ -403,8 +403,15 @@ void global_dirty_limits(unsigned long *
> > else
> > background = (dirty_background_ratio * available_memory) / 100;
> >
> > - if (background >= dirty)
> > - background = dirty / 2;
> > + /*
> > + * Ensure at least 1/4 gap between background and dirty thresholds, so
> > + * that when dirty throttling starts at (background + dirty)/2, it's at
> > + * the entrance of bdi soft throttle threshold, so as to avoid being
> > + * hard throttled.
> > + */
> > + if (background > dirty - dirty * 2 / BDI_SOFT_DIRTY_LIMIT)
> > + background = dirty - dirty * 2 / BDI_SOFT_DIRTY_LIMIT;
> > +
> > tsk = current;
> > if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
> > background += background / 4;
>
>
> Hrm,.. the alternative is to return -ERANGE or somesuch when people try
> to write nonsensical values.
>
> I'm not sure what's best, guessing at what the user did mean to do or
> forcing him to actually think.
Yes, this may break user space either way.
Doing it loudly does make more sense.
Thanks,
Fengguang
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^ permalink raw reply [flat|nested] 4+ messages in thread
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2010-11-17 4:27 ` [PATCH 10/13] writeback: make reasonable gap between the dirty/background thresholds Wu Fengguang
2010-11-24 11:18 ` Peter Zijlstra
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