linux-kernel - Re: [PATCH] vmscan: limit concurrent reclaimers in shrink

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Date:	Fri, 11 Dec 2009 23:08:42 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	lwoodman@...hat.com, kosaki.motohiro@...fujitsu.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, aarcange@...hat.com
Subject: Re: [PATCH] vmscan: limit concurrent reclaimers in shrink_zone

On Fri, Dec 11, 2009 at 10:51 PM, Rik van Riel <riel@...hat.com> wrote:
> On 12/11/2009 08:41 AM, Minchan Kim wrote:
>>
>> Hi, Larry.
>>
>> On Fri, Dec 11, 2009 at 9:07 PM, Larry Woodman<lwoodman@...hat.com>
>>  wrote:
>>>
>>> Minchan Kim wrote:
>>>>
>>>> I like this. but why do you select default value as constant 8?
>>>> Do you have any reason?
>>>>
>>>> I think it would be better to select the number proportional to NR_CPU.
>>>> ex) NR_CPU * 2 or something.
>>>>
>>>> Otherwise looks good to me.
>>>>
>>>> Reviewed-by: Minchan Kim<minchan.kim@...il.com>
>>>>
>>>>
>>>
>>> This is a per-zone count so perhaps a reasonable default is the number of
>>> CPUs on the
>>> NUMA node that the zone resides on ?
>>
>> For example, It assume one CPU per node.
>> It means your default value is 1.
>> On the CPU, process A try to reclaim HIGH zone.
>> Process B want to reclaim NORMAL zone.
>> But Process B can't enter reclaim path sincev throttle default value is 1
>> Even kswap can't reclaim.
>
> 1) the value is per zone, so process B can go ahead

Sorry. I misunderstood Larry's point.
I though Larry mentioned global limit not per zone.

> 2) kswapd is always excempt from this limit, since
>   there is only 1 kswapd per node anyway

Larry could test with Rik's patch for what's good default value.
If it proves NR_CPU on node is proper as default value,
We can change default value with it.


> --
> All rights reversed.
>



-- 
Kind regards,
Minchan Kim
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