[patch] memory reclaim more efficiently

[patch] memory reclaim more efficiently

[Takenori Nagano]

Hi,

Efficiency of memory reclaim is recently one of the hot topics. (LRU splitting,
pageout throttling, etc...) I would like to contribute it and I made this patch.

In shrink_zone(), system can not return to user mode before it finishes to
search LRU list. IMHO, it is very wasteful, since the user processes stay
unnecessarily long time in shrink_zone() loop and application response time
becomes relatively bad. This patch changes shrink_zone() that it finishes memory
reclaim when it reclaims enough memory.

the conditions to end searching:

1. order of request page is 0
2. process is not kswapd.
3. satisfy the condition to return try_to_free_pages()
   # nr_reclaim > SWAP_CLUSTER_MAX


Signed-off-by: Takenori Nagano <t-nagano@ah.jp.nec.com>
Signed-off-by: Keiichi Kii <k-keiichi@bx.jp.nec.com>

---
diff -uprN linux-2.6.26-rc6.orig/mm/vmscan.c linux-2.6.26-rc6/mm/vmscan.c
--- linux-2.6.26-rc6.orig/mm/vmscan.c	2008-06-13 06:22:24.000000000 +0900
+++ linux-2.6.26-rc6/mm/vmscan.c	2008-06-20 15:05:03.492700863 +0900
@@ -1224,6 +1224,9 @@ static unsigned long shrink_zone(int pri
 			nr_reclaimed += shrink_inactive_list(nr_to_scan, zone,
 								sc);
 		}
+		if (nr_reclaimed > sc->swap_cluster_max && !sc->order
+						&& !current_is_kswapd())
+			break;
 	}
 
 	throttle_vm_writeout(sc->gfp_mask);




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Re: [patch] memory reclaim more efficiently

[KOSAKI Motohiro]

Hi nagano-san,

> In shrink_zone(), system can not return to user mode before it finishes to
> search LRU list. IMHO, it is very wasteful, since the user processes stay
> unnecessarily long time in shrink_zone() loop and application response time
> becomes relatively bad. This patch changes shrink_zone() that it finishes memory
> reclaim when it reclaims enough memory.
> 
> the conditions to end searching:
> 
> 1. order of request page is 0
> 2. process is not kswapd.
> 3. satisfy the condition to return try_to_free_pages()
>    # nr_reclaim > SWAP_CLUSTER_MAX

I have 3 question.

1. Do you have any performance number?
2. I think this patch advocate many try_to_free_pages() called is better than
   one try_to_free_page waste long time. right?
   and, why do you think so?
3. if this patch improve perfomance, I guess DEF_PRIORITY is
   too small on your machine.
   if DEF_PRIORITY is proportional to system memory, do your problem are solved?



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Re: [patch] memory reclaim more efficiently

[Takenori Nagano]

KOSAKI Motohiro wrote:
> > Hi nagano-san,
> >
>> >> In shrink_zone(), system can not return to user mode before it finishes to
>> >> search LRU list. IMHO, it is very wasteful, since the user processes stay
>> >> unnecessarily long time in shrink_zone() loop and application response time
>> >> becomes relatively bad. This patch changes shrink_zone() that it finishes
memory
>> >> reclaim when it reclaims enough memory.
>> >>
>> >> the conditions to end searching:
>> >>
>> >> 1. order of request page is 0
>> >> 2. process is not kswapd.
>> >> 3. satisfy the condition to return try_to_free_pages()
>> >>    # nr_reclaim > SWAP_CLUSTER_MAX

Hi Kosaki-san,

> > I have 3 question.
> >
> > 1. Do you have any performance number?

I tested some, but I don't collect data.  :-(
I will test again and post results.

> > 2. I think this patch advocate many try_to_free_pages() called is better than
> >    one try_to_free_page waste long time. right?
> >    and, why do you think so?

I think user process is stopped long time on memory reclaim is not good.
It is enough for user process to reclaim memory is needed. We have kswapd memory
reclaim daemon. I think memory reclaim is kswapd's job.

> > 3. if this patch improve perfomance, I guess DEF_PRIORITY is
> >    too small on your machine.
> >    if DEF_PRIORITY is proportional to system memory, do your problem are solved?

Your idea is so nice.  :-)
IMHO, it is not perfect if reclaimable memory is not on front.

Thanks,
  Takenori

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