Re: compaction: trying to understand the code

[Minchan Kim <minchan.kim@gmail.com>]

On Mon, Aug 23, 2010 at 4:16 PM, Mel Gorman <mel@csn.ul.ie> wrote:
> On Mon, Aug 23, 2010 at 12:31:21AM +0900, Minchan Kim wrote:
>> <SNIP>
>>
>> From 560e8898295c663f02aede07b3d55880eba16c69 Mon Sep 17 00:00:00 2001
>> 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.
>>
>> Cc: Mel Gorman <mel@csn.ul.ie>
>> Cc: Wu Fengguang <fengguang.wu@intel.com>
>> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
>
> Seems reasonable to me.
>
> Acked-by: Mel Gorman <mel@csn.ul.ie>

Thanks.

>
> Want to repost this as a standalone patch?

Yes. It is enough to be a standalone.
I will repost the patch as removing part about reporting Iram's problem.

We need to dig in Iram's problem regardless of this patch.

-- 
Kind regards,
Minchan Kim

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