Re: [RFC 2/3] vmscan hook

[Rik van Riel <riel@redhat.com>]

On 01/18/2012 09:25 PM, KAMEZAWA Hiroyuki wrote:
> On Wed, 18 Jan 2012 09:17:17 -0500
> Rik van Riel<riel@redhat.com>  wrote:
>
>> On 01/17/2012 07:18 PM, KAMEZAWA Hiroyuki wrote:
>>> On Wed, 18 Jan 2012 08:08:01 +0900
>>> Minchan Kim<minchan@kernel.org>   wrote:
>>>
>>>>>>> 2. can't we measure page-in/page-out distance by recording something ?
>>>>>>
>>>>>> I can't understand your point. What's relation does it with swapout prevent?
>>>>>>
>>>>>
>>>>> If distance between pageout ->   pagein is short, it means thrashing.
>>>>> For example, recoding the timestamp when the page(mapping, index) was
>>>>> paged-out, and check it at page-in.
>>>>
>>>> Our goal is prevent swapout. When we found thrashing, it's too late.
>>>
>>> If you want to prevent swap-out, don't swapon any. That's all.
>>> Then, you can check the number of FILE_CACHE and have threshold.
>>
>> I think you are getting hung up on a word here.
>>
>> As I understand it, the goal is to push out the point where
>> we start doing heavier swap IO, allowing us to overcommit
>> memory more heavily before things start really slowing down.
>>
>
> Yes.
>
> Hmm, considering that the issue is slow down,
>
> time values as
>
> - 'cpu time used for memory reclaim'
> - 'latency of page allocation'
> - 'application execution speed' ?
>
> may be a better score to see rather than just seeing lru's stat.

I believe those all qualify as "too late".

We want to prevent things from becoming bad, for as long
as we (easily) can.

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