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Date: Fri, 15 Sep 2006 11:21:39 +0400
From: Pavel Emelianov <xemul@openvz.org>
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To: sekharan@us.ibm.com
CC: balbir@in.ibm.com, Srivatsa <vatsa@in.ibm.com>,
       Kirill Korotaev <dev@sw.ru>, Rik van Riel <riel@redhat.com>,
       CKRM-Tech <ckrm-tech@lists.sourceforge.net>,
       Dave Hansen <haveblue@us.ibm.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Andi Kleen <ak@suse.de>, Christoph Hellwig <hch@infradead.org>,
       Andrey Savochkin <saw@sw.ru>, devel@openvz.org,
       Matt Helsley <matthltc@us.ibm.com>, Hugh Dickins <hugh@veritas.com>,
       Alexey Dobriyan <adobriyan@mail.ru>, Oleg Nesterov <oleg@tv-sign.ru>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [ckrm-tech] [PATCH] BC: resource beancounters (v4) (added	user
 memory)
References: <44FD918A.7050501@sw.ru>	<44FDAB81.5050608@in.ibm.com>	 <44FEC7E4.7030708@sw.ru>	<44FF1EE4.3060005@in.ibm.com>	 <1157580371.31893.36.camel@linuxchandra>	<45011CAC.2040502@openvz.org>	 <1157730221.26324.52.camel@localhost.localdomain>	 <4501B5F0.9050802@in.ibm.com> <450508BB.7020609@openvz.org>	 <4505161E.1040401@in.ibm.com> <45051AC7.2000607@openvz.org>	 <1158000590.6029.33.camel@linuxchandra>	<45069072.4010007@openvz.org>	 <1158105488.4800.23.camel@linuxchandra>	<4507BC11.6080203@openvz.org>	 <1158186664.18927.17.camel@linuxchandra> <45090A6E.1040206@openvz.org>	 <45090D9E.9000903@in.ibm.com>  <450952F8.8080606@openvz.org> <1158278541.6357.49.camel@linuxchandra>
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Chandra Seetharaman wrote:
> On Thu, 2006-09-14 at 17:02 +0400, Pavel Emelianov wrote:
>
> <snip>
>   
>> Reserving in advance means that sometimes you won't be able to start a
>> new group without taking back some of reserved pages. This is ... strange.
>>     
>
> I do not see it strange. At the time of creation, user sees the failure
> (that there isn't enough resource to provide the required/requested
> guarantee) and can act accordingly.
>
> BTW, VMware does it this way.
>   
And VPS density in VMware is MUCH lower than in
OpenVZ with beancounters :)
>   
>> I think that a satisfactory solution now would be:
>>  - limit unreclaimable memory during mmap() against soft limit to prevent
>>    potential rejects during page faults;
>>     
>
> we can have guarantee and still handle it this way.
>   
>>  - reclaim memory in case of hitting hard limit;
>>  - guarantees are done via setting soft and hard limits as I've shown
>> before.
>>     
>
> complexity is high in doing that.
>   
Nope. I've already said in another letter that a program of 60 lines
does this in a single loop.
>> The question still open is wether or not to account fractions.
>> I propose to skip fractions for a while and try to charge the page to
>> it's first user.
>>     
>
> sounds fine
>
>   
>> So final BC design is:
>> 1. three resources:
>>        - kernel memory
>>        - user unreclaimable memory
>>        - user reclaimable memory
>>     
>
> should be able to get other controllers also under this framework.
>   
OK. But note, that it's easy to add new resource to current BC code.
The most difficult thing is placing 'charge/uncharge' calls over the kernel.
>   
>> 2. unreclaimable memory is charged "in advance", reclaimable
>>    is charged "on demand" with reclamation if needed
>> 3. each object (kernel one or user page) is charged to the
>>    first user
>> 4. each resource controller declares it's own
>>        - meaning of "limit" parameter (percent/size/bandwidth/etc)
>>        - behaviour on changing limit (e.g. reclamation)
>>        - behaviour on hitting the limit (e.g. reclamation)
>> 5. BC can be assigned to any task by pid (not just current)
>>    without recharging currently charged resources.
>>     
>
> Please see the emails i sent earlier in this context:
> http://marc.theaimsgroup.com/?l=ckrm-tech&m=115593001810616&w=2
>
> We would need at least:
>  - BC should be created/deleted explicitly by the user
>  - cleaner interface for controller writers
>   
OK.
Next week we'll try to send a new set of patches.
-
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