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Date: Thu, 10 Sep 2009 00:39:02 +0900
Message-ID: <28c262360909090839j626ff818of930cf13a6185123@mail.gmail.com>
Subject: Re: [rfc] lru_add_drain_all() vs isolation
From: Minchan Kim <minchan.kim@gmail.com>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, Mike Galbraith <efault@gmx.de>,
       Ingo Molnar <mingo@elte.hu>, linux-mm <linux-mm@kvack.org>,
       Oleg Nesterov <onestero@redhat.com>,
       lkml <linux-kernel@vger.kernel.org>
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On Wed, Sep 9, 2009 at 1:27 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
>> The usefulness of a scheme like this requires:
>>
>> 1. There are cpus that continually execute user space code
>> ? ?without system interaction.
>>
>> 2. There are repeated VM activities that require page isolation /
>> ? ?migration.
>>
>> The first page isolation activity will then clear the lru caches of the
>> processes doing number crunching in user space (and therefore the first
>> isolation will still interrupt). The second and following isolation will
>> then no longer interrupt the processes.
>>
>> 2. is rare. So the question is if the additional code in the LRU handling
>> can be justified. If lru handling is not time sensitive then yes.
>
> Christoph, I'd like to discuss a bit related (and almost unrelated) thing.
> I think page migration don't need lru_add_drain_all() as synchronous, because
> page migration have 10 times retry.
>
> Then asynchronous lru_add_drain_all() cause
>
> ?- if system isn't under heavy pressure, retry succussfull.
> ?- if system is under heavy pressure or RT-thread work busy busy loop, retry failure.
>
> I don't think this is problematic bahavior. Also, mlock can use asynchrounous lru drain.

I think, more exactly, we don't have to drain lru pages for mlocking.
Mlocked pages will go into unevictable lru due to
try_to_unmap when shrink of lru happens.
How about removing draining in case of mlock?

>
> What do you think?
>
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
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>



-- 
Kind regards,
Minchan Kim
--
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