Re: [RFC][PATCH] the proposal of improve page reclaim by throttle

[minchan Kim]

On Thu, Feb 21, 2008 at 7:55 PM, KOSAKI Motohiro
<kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
> Hi Kim-san,
>
>  Thank you very much.
>  btw, what different between <test 1> and <test 2>?

<test 1> have no swap device with 200 tasks by hackbench.
But <test 2> have swap device(32M) with 240 tasks by hackbench.
If <test2> have no swap device without your patch, <test2> is killed by OOM.

<test 1> - NO SWAP
Running with 5*40 (== 200) tasks.
...
<test 2> - SWAP
Running with 6*40 (== 240) tasks.
...

>
>  >  It was a very interesting result.
>  >  In embedded system, your patch improve performance a little in case
>  >  without noswap(normal case in embedded system).
>  >  But, more important thing is OOM occured when I made 240 process
>  >  without swap device and vanilla kernel.
>  >  Then, I applied your patch, it worked very well without OOM.
>
>  Wow, it is very interesting result!
>  I am very happy.
>
>
>  >  I think that's why zone's page_scanned was six times greater than
>  >  number of lru pages.
>  >  At result, OOM happened.
>
>  please repost question with change subject.
>  i don't know reason of vanilla kernel behavior, sorry.

Normally, embedded linux have only one zone(DMA).

If your patch isn't applied, several processes can reclaim memory in parallel.
then, DMA zone's pages_scanned is suddenly increased largely. Because
embedded linux have no swap device,  kernel can't stop to scan lru
list until meeting page cache page. so if zone->pages_scanned is
greater six time than lru list pages, kernel make the zone with
unreclaimable state, As a result, OOM will kill it, too.

-- 
Thanks,
barrios
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