Re: [PATCH v4 2/7] deactivate invalidated pages

[Minchan Kim <minchan.kim@gmail.com>]

On Wed, Dec 8, 2010 at 3:56 PM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> * MinChan Kim <minchan.kim@gmail.com> [2010-12-08 11:15:19]:
>
>> On Wed, Dec 8, 2010 at 10:56 AM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> > On Wed, 8 Dec 2010 10:43:08 +0900
>> > Minchan Kim <minchan.kim@gmail.com> wrote:
>> >
>> >> Hi Kame,
>> >>
>> > Hi,
>> >
>> >> > I wonder ...how about adding "victim" list for "Reclaim" pages ? Then, we don't need
>> >> > extra LRU rotation.
>> >>
>> >> It can make the code clean.
>> >> As far as I think, victim list does following as.
>> >>
>> >> 1. select victim pages by strong hint
>> >> 2. move the page from LRU to victim
>> >> 3. reclaimer always peeks victim list before diving into LRU list.
>> >> 4-1. If the victim pages is used by others or dirty, it can be moved
>> >> into LRU, again or remain the page in victim list.
>> >> If the page is remained victim, when do we move it into LRU again if
>> >> the reclaimer continues to fail the page?
>> > When sometone touches it.
>> >
>> >> We have to put the new rule.
>> >> 4-2. If the victim pages isn't used by others and clean, we can
>> >> reclaim the page asap.
>> >>
>> >> AFAIK, strong hints are just two(invalidation, readahead max window heuristic).
>> >> I am not sure it's valuable to add new hierarchy(ie, LRU, victim,
>> >> unevictable) for cleaning the minor codes.
>> >> In addition, we have to put the new rule so it would make the LRU code
>> >> complicated.
>> >> I remember how unevictable feature merge is hard.
>> >>
>> > yes, it was hard.
>> >
>> >> But I am not against if we have more usecases. In this case, it's
>> >> valuable to implement it although it's not easy.
>> >>
>> >
>> > I wonder "victim list" can be used for something like Cleancache, when
>> > we have very-low-latency backend devices.
>> > And we may able to have page-cache-limit, which Balbir proposed as.
>>
>> Yes, I thought that, too. I think it would be a good feature in embedded system.
>>
>> >
>> >  - kvictimed? will move unmappedd page caches to victim list
>> > This may work like a InactiveClean list which we had before and make
>> > sizing easy.
>> >
>>
>> Before further discuss, we need customer's confirm.
>> We know very well it is very hard to merge if anyone doesn't use.
>>
>> Balbir, What do think about it?
>>
>
> The idea seems interesting, I am in the process of refreshing my
> patches for unmapped page cache control. I presume the process of
> filling the victim list will be similar to what I have or unmapped
> page cache isolation.

I saw your previous implementation. It doesn't have any benefit from
victim list.
It needs scanning pfns, select unmapped page and move it into victim list.
I think we might need kvictimd as Kame said but I am not convinced.
If I have a trouble with implementing my series, I might think it. But
until now, I think it's not bad and rough test result isn't bad.

To be honest, I think victim list(or cleanlist) is to be another
project. If it is completed, maybe we can make my patches simple.
I approve page cache limit control POV but it should be another project.
So I want to merge this series then if we need really victim list,
let's consider at that time.

Anyway, I will see your next version to find needs of victim list.

>
>>
>> > Thanks,
>> > -Kame
>> >
>> >
>> >
>> >
>>
>>
>>
>> --
>> Kind regards,
>> Minchan Kim
>
> --
>        Three Cheers,
>        Balbir
>



-- 
Kind regards,
Minchan Kim

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