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

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Date:	Fri, 11 Dec 2009 12:43:50 +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 12:19 PM, Rik van Riel <riel@...hat.com> wrote:
> On 12/10/2009 09:03 PM, Minchan Kim wrote:
>
>>> +The default value is 8.
>>> +
>>> +=============================================================
>>
>> 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.
>
> Pessimistically, I assume that the pageout code spends maybe
> 10% of its time on locking (we have seen far, far worse than
> this with thousands of processes in the pageout code).  That
> means if we have more than 10 threads in the pageout code,
> we could end up spending more time on locking and less doing
> real work - slowing everybody down.

Thanks for giving precious information to me. :

We always have a question magic value with no comment.

Actually I don't want to add another magic value without comment.
so I would like to add the your good explanation in change log
or as comment on code.

>
> I rounded it down to the closest power of 2 to come up with
> an arbitrary number that looked safe :)
>
> However, this number is per zone - I imagine that really large
> systems will have multiple memory zones, so they can run with
> more than 8 processes in the pageout code simultaneously.
>
>> Reviewed-by: Minchan Kim<minchan.kim@...il.com>
>
> Thank you.

Thanks for quick reply. :)

> --
> All rights reversed.
>



-- 
Kind regards,
Minchan Kim
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