[PATCH] mm/vmscan.c: avoid scanning the whole targets[*] when scan_balance equals SCAN_FILE/SCAN_ANON

[PATCH] mm/vmscan.c: avoid scanning the whole targets[*] when scan_balance equals SCAN_FILE/SCAN_ANON

[Chen Yucong]

If (scan_balance == SCAN_FILE) is true for shrink_lruvec, then  the value of
targets[LRU_INACTIVE_ANON] and targets[LRU_ACTIVE_ANON] will be zero. As a result,
the value of 'percentage' will also be  zero, and the *whole* targets[LRU_INACTIVE_FILE]
and targets[LRU_ACTIVE_FILE] will be scanned.

For (scan_balance == SCAN_ANON), there is the same conditions stated above.

But via https://lkml.org/lkml/2013/4/10/334, we can find that the kernel does not prefer
reclaiming too many pages from the other LRU. So before recalculating the other LRU scan
count based on its original scan targets and the percentage scanning already complete, we
should need to check whether 'scan_balance' equals SCAN_FILE/SCAN_ANON.

Signed-off-by: Chen Yucong <slaoub@gmail.com>
---
 mm/vmscan.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d51f7e0..ca3f5f1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2120,6 +2120,9 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 			percentage = nr_file * 100 / scan_target;
 		}
 
+		if (targets[lru] == 0 && targets[lru + LRU_ACTIVE] == 0)
+			break;
+
 		/* Stop scanning the smaller of the LRU */
 		nr[lru] = 0;
 		nr[lru + LRU_ACTIVE] = 0;
-- 
1.7.10.4

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH] mm/vmscan.c: avoid scanning the whole targets[*] when scan_balance equals SCAN_FILE/SCAN_ANON

[Johannes Weiner]

Hi Chen,

On Fri, Jun 06, 2014 at 04:54:26PM +0800, Chen Yucong wrote:
> If (scan_balance == SCAN_FILE) is true for shrink_lruvec, then  the value of
> targets[LRU_INACTIVE_ANON] and targets[LRU_ACTIVE_ANON] will be zero. As a result,
> the value of 'percentage' will also be  zero, and the *whole* targets[LRU_INACTIVE_FILE]
> and targets[LRU_ACTIVE_FILE] will be scanned.
> 
> For (scan_balance == SCAN_ANON), there is the same conditions stated above.
> 
> But via https://lkml.org/lkml/2013/4/10/334, we can find that the kernel does not prefer
> reclaiming too many pages from the other LRU. So before recalculating the other LRU scan
> count based on its original scan targets and the percentage scanning already complete, we
> should need to check whether 'scan_balance' equals SCAN_FILE/SCAN_ANON.
> 
> Signed-off-by: Chen Yucong <slaoub@gmail.com>
> ---
>  mm/vmscan.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index d51f7e0..ca3f5f1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2120,6 +2120,9 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>  			percentage = nr_file * 100 / scan_target;
>  		}
>  
> +		if (targets[lru] == 0 && targets[lru + LRU_ACTIVE] == 0)
> +			break;

We have meanwhile included a change that bails out if nr_anon or
nr_file are zero, right before that percentage calculation, that
should cover the scenario you're describing.  It's called:

mm: vmscan: use proportional scanning during direct reclaim and full scan at DEF_PRIORITY

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH] mm/vmscan.c: avoid scanning the whole targets[*] when scan_balance equals SCAN_FILE/SCAN_ANON

[Chen Yucong]

On Fri, 2014-06-06 at 09:12 -0400, Johannes Weiner wrote:
> Hi Chen,
> 
> On Fri, Jun 06, 2014 at 04:54:26PM +0800, Chen Yucong wrote:
> > If (scan_balance == SCAN_FILE) is true for shrink_lruvec, then  the value of
> > targets[LRU_INACTIVE_ANON] and targets[LRU_ACTIVE_ANON] will be zero. As a result,
> > the value of 'percentage' will also be  zero, and the *whole* targets[LRU_INACTIVE_FILE]
> > and targets[LRU_ACTIVE_FILE] will be scanned.
> > 
> > For (scan_balance == SCAN_ANON), there is the same conditions stated above.
> > 
> > But via https://lkml.org/lkml/2013/4/10/334, we can find that the kernel does not prefer
> > reclaiming too many pages from the other LRU. So before recalculating the other LRU scan
> > count based on its original scan targets and the percentage scanning already complete, we
> > should need to check whether 'scan_balance' equals SCAN_FILE/SCAN_ANON.
> > 
> > Signed-off-by: Chen Yucong <slaoub@gmail.com>
> > ---
> >  mm/vmscan.c |    3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index d51f7e0..ca3f5f1 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -2120,6 +2120,9 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
> >  			percentage = nr_file * 100 / scan_target;
> >  		}
> >  
> > +		if (targets[lru] == 0 && targets[lru + LRU_ACTIVE] == 0)
> > +			break;
> 
> We have meanwhile included a change that bails out if nr_anon or
> nr_file are zero, right before that percentage calculation, that
> should cover the scenario you're describing.  It's called:
> 
> mm: vmscan: use proportional scanning during direct reclaim and full scan at DEF_PRIORITY

Thanks very much for your reply. Indeed, your patch is more
comprehensive and perfect. I think I need to update my local
git-repository timely.

thx!
cyc 

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>