Re: compaction: trying to understand the code

From: Minchan Kim <minchan.kim@gmail.com>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>,
	Andrew Morton <akpm@linux-foundation.org>,
	Iram Shahzad <iram.shahzad@jp.fujitsu.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: compaction: trying to understand the code
Date: Mon, 23 Aug 2010 10:58:09 +0900	[thread overview]
Message-ID: <AANLkTim8c5C+vH1HUx-GsScirmnVoJXenLST1qQgk2bp@mail.gmail.com> (raw)
In-Reply-To: <20100822232316.GA339@localhost>

On Mon, Aug 23, 2010 at 8:23 AM, Wu Fengguang <fengguang.wu@intel.com> wrote:
>> From: Minchan Kim <minchan.kim@gmail.com>
>> Date: Mon, 23 Aug 2010 00:20:44 +0900
>> Subject: [PATCH] compaction: handle active and inactive fairly in too_many_isolated
>>
>> Iram reported compaction's too_many_isolated loops forever.
>> (http://www.spinics.net/lists/linux-mm/msg08123.html)
>>
>> The meminfo of situation happened was inactive anon is zero.
>> That's because the system has no memory pressure until then.
>> While all anon pages was in active lru, compaction could select
>> active lru as well as inactive lru. That's different things
>> with vmscan's isolated. So we has been two too_many_isolated.
>>
>> While compaction can isolated pages in both active and inactive,
>> current implementation of too_many_isolated only considers inactive.
>> It made Iram's problem.
>>
>> This patch handles active and inactie with fair.
>> That's because we can't expect where from and how many compaction would
>> isolated pages.
>>
>> This patch changes (nr_isolated > nr_inactive) with
>> nr_isolated > (nr_active + nr_inactive) / 2.
>
> The change looks good, thanks. However I'm not sure if it's enough.

Thanks.

>
> I wonder where the >40MB isolated pages come about.  inactive_anon
> remains 0 and free remains high over a long time, so it seems there
> are no concurrent direct reclaims at all. Are the pages isolated by
> the compaction process itself?

Agree. I wonder too.

Now compaction isolates page per 32 until reaching pageblock_nr_pages,
So I can't understand how 40MB isolated pages come out.

Iram. How do you execute test_app?

1) synchronous test
1.1 start test_app
1.2 wait test_app job done (ie, wait memory is fragment)
1.3 echo 1 > /proc/sys/vm/compact_memory

2) asynchronous test
2.1 start test_app
2.2 not wait test_app job done
2.3 echo 1 > /proc/sys/vm/compact_memory(Maybe your test app and
compaction were executed parallel)

Which one is your scenario?

>
> Thanks,
> Fengguang
>

-- 
Kind regards,
Minchan Kim

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