Re: [LSF/MM TOPIC] Writeback - current state and future

["Sorin Faibish" <sfaibish@emc.com>]

Jan,

It looks like people in LSF are not so interested in writeback problems
and we will not have a discussion on this. Too bad as I have new results
to present regarding the latest patches in the kernel related to writeback
and I am not sure for the best.

/Sorin


On Fri, 11 Feb 2011 11:22:18 -0500, sfaibish <sfaibish@emc.com> wrote:

> On Fri, 11 Feb 2011 09:47:17 -0500, Jan Kara <jack@suse.cz> wrote:
>
>> On Sun 06-02-11 10:13:41, Sorin Faibish wrote:
>>> I was thinking to have a special track for all the writeback related
>>> topics.
>>   Well, a separate track might be a bit too much I feel ;). I'm  
>> interested
>> also in other things that are happening... We'll see what the program  
>> will
>> be but I can imagine we can discuss for a couple of hours but that  
>> might be
>> just a discussion in a small circle over a <enter preferable drink>.
> No problem. I pay for the beer. :) You make the expert pick.
>
>>
>>> I would like also to include a discussion on new cache writeback  
>>> paterns
>>> with the target to prevent any cache swaps that are becoming a
>>> bigger problem
>>> when dealing with servers wir 100's GB caches. The swap is the worst  
>>> that
>>> could happen to the performance of such systems. I will share my
>>> latest findings
>>> in the cache writeback in continuation to my previous discussion at
>>> last LSF.
>>   I'm not sure what do you exactly mean by 'cache swaps'. If you mean  
>> that
>> your application private cache is swapped out, then I can imagine this  
>> is a
>> problem but I'd need more details to tell how big.
> What I meant is to prevent any global cache swap. Think that you have to  
> SWAP
> 256GB of cache to a 120MB/sec SATA disk. How long it will take? Cannot be
> tolerated. Even if you use SSD at say 1GB/sec it is still a long time.  
> Not
> typical but common in HPC. I am not sure you saw my latest results but I
> had an example where the swap was taking a long time to the point that a
> build on a small memory system didn't finish. The good news are that the
> latest kernels 37 RC3 made progress. I have additional data to present.
> I will present the latest results next week at FAST conference.
>
> /Sorin
>
>>
>> 									Honza
>
>
>



-- 
Best Regards
Sorin Faibish
Corporate Distinguished Engineer
Unified Storage Division

        EMC2
where information lives

Phone: 508-435-1000 x 48545
Cellphone: 617-510-0422
Email : sfaibish@emc.com

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