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

[sfaibish <sfaibish@emc.com>]

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: 508-249-5745
Cellphone: 617-510-0422
Email : sfaibish@emc.com

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