Re: [PATCH] mm: check zone->all_unreclaimable in all_unreclaimable()

[Minchan Kim]

Hi Kame,

Sorry for late response.
I had a time to test this issue shortly because these day I am very busy.
This issue was interesting to me.
So I hope taking a time for enough testing when I have a time.
I should find out root cause of livelock.

I will answer your comment after it. :)
Thanks!

On Wed, Mar 9, 2011 at 2:37 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> On Tue, 8 Mar 2011 08:45:51 +0900
> Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
>
>> On Tue, Mar 8, 2011 at 6:58 AM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>> > On Sun, 6 Mar 2011 02:07:59 +0900
>> > Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
>> > Any alternative proposals? ÂWe should get the livelock fixed if possible..
>> >
>>
>> And we should avoid unnecessary OOM kill if possible.
>>
>> I think the problem is caused by (zone->pages_scanned <
>> zone_reclaimable_pages(zone) * 6). I am not sure (* 6) is a best. It
>> would be rather big on recent big DRAM machines.
>>
>
> It means 3 times full-scan from the highest priority to the lowest
> and cannot freed any pages. I think big memory machine tend to have
> more cpus, so don't think it's big.
>
>> I think it is a trade-off between latency and OOM kill.
>> If we decrease the magic value, maybe we should prevent the almost
>> livelock but happens unnecessary OOM kill.
>>
>
> Hmm, should I support a sacrifice feature 'some signal(SIGINT?) will be sent by
> the kernel when it detects system memory is in short' in cgroup ?
> (For example, if full LRU scan is done in a zone, notifier
> Âworks and SIGINT will be sent.)
>
>> And I think zone_reclaimable not fair.
>> For example, too many scanning makes reclaimable state to
>> unreclaimable state. Maybe it takes a very long time. But just some
>> page free makes unreclaimable state to reclaimabe with very easy. So
>> we need much painful reclaiming for changing reclaimable state with
>> unreclaimabe state. it would affect latency very much.
>>
>> Maybe we need more smart zone_reclaimabe which is adaptive with memory pressure.
>>
> I agree.
>
> Thanks,
> -Kame
>
>



-- 
Kind regards,
Minchan Kim
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