linux-kernel - Re: Over-eager swapping

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Date:	Tue, 3 Aug 2010 13:47:36 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Chris Webb <chris@...chsys.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: Over-eager swapping

On Tue, Aug 3, 2010 at 1:28 PM, Wu Fengguang <fengguang.wu@...el.com> wrote:
> On Tue, Aug 03, 2010 at 12:09:18PM +0800, Minchan Kim wrote:
>> On Tue, Aug 3, 2010 at 12:31 PM, Chris Webb <chris@...chsys.com> wrote:
>> > Minchan Kim <minchan.kim@...il.com> writes:
>> >
>> >> Another possibility is _zone_reclaim_ in NUMA.
>> >> Your working set has many anonymous page.
>> >>
>> >> The zone_reclaim set priority to ZONE_RECLAIM_PRIORITY.
>> >> It can make reclaim mode to lumpy so it can page out anon pages.
>> >>
>> >> Could you show me /proc/sys/vm/[zone_reclaim_mode/min_unmapped_ratio] ?
>> >
>> > Sure, no problem. On the machine with the /proc/meminfo I showed earlier,
>> > these are
>> >
>> >  # cat /proc/sys/vm/zone_reclaim_mode
>> >  0
>> >  # cat /proc/sys/vm/min_unmapped_ratio
>> >  1
>>
>> if zone_reclaim_mode is zero, it doesn't swap out anon_pages.
>
> If there are lots of order-1 or higher allocations, anonymous pages
> will be randomly evicted, regardless of their LRU ages. This is

I thought swapped out page is huge (ie, 3G) even though it enters lumpy mode.
But it's possible. :)

> probably another factor why the users claim. Are there easy ways to
> confirm this other than patching the kernel?

cat /proc/buddyinfo can help?

Off-topic:
It would be better to add new vmstat of lumpy entrance.

Pseudo code.

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0f9f624..d10ff4e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1641,7 +1641,7 @@ out:
        }
 }

-static void set_lumpy_reclaim_mode(int priority, struct scan_control *sc)
+static void set_lumpy_reclaim_mode(int priority, struct scan_control
*sc, struct zone *zone)
 {
        /*
         * If we need a large contiguous chunk of memory, or have
@@ -1654,6 +1654,9 @@ static void set_lumpy_reclaim_mode(int priority,
struct scan_control *sc)
                sc->lumpy_reclaim_mode = 1;
        else
                sc->lumpy_reclaim_mode = 0;
+
+       if (sc->lumpy_reclaim_mode)
+               inc_zone_state(zone, NR_LUMPY);
 }

 /*
@@ -1670,7 +1673,7 @@ static void shrink_zone(int priority, struct zone *zone,

        get_scan_count(zone, sc, nr, priority);

-       set_lumpy_reclaim_mode(priority, sc);
+       set_lumpy_reclaim_mode(priority, sc, zone);

        while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
                                        nr[LRU_INACTIVE_FILE]) {

-- 
Kind regards,
Minchan Kim
--
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