linux-kernel - Re: [PATCH 4/4] compcache: documentation

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Message-ID: <20090828195303.GA4889@balbir.in.ibm.com>
Date:	Sat, 29 Aug 2009 01:23:03 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Nitin Gupta <ngupta@...are.org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-mm-cc@...top.org
Subject: Re: [PATCH 4/4] compcache: documentation

* Nitin Gupta <ngupta@...are.org> [2009-08-25 23:41:06]:

> On 08/25/2009 10:33 PM, Balbir Singh wrote:
>
>
>>> +It consists of three modules:
>>> + - xvmalloc.ko: memory allocator
>>
>> I've seen your case for a custom allocator, but why can't we
>>
>> 1) Refactor slob and use it
>
> SLOB is fundamentally a different allocator. It looked at it in detail
> but could not image how can I make it suitable for the project. SLOB
> really does not fit it.
>
>> 2) Do we care about the optimizations in SLUB w.r.t. scalability in
>> your module? If so.. will xvmalloc meet those requirements?
>>
>
> Scalability is desired which xvmalloc lacks in its current state. My
> plan is to have a wrapper around xvmalloc that creates per-cpu pools
> and leave xvmalloc core simple. Along with this, detailed profiling
> needs to be done to see where the bottlenecks are in the core itself.
>

I've not yet tested the patches, but adding another allocator does
worry me a bit. Do you intend to allow other users to consume the
allocator routines?

>
>>
>> What level of compression have you observed? Any speed trade-offs?
>>
>
> All the performance numbers can be found at:
> http://code.google.com/p/compcache/wiki/Performance
>
> I also summarized these in patch [0/4]:
> http://lkml.org/lkml/2009/8/24/8
>
> The compression ratio is highly workload dependent. On "generic" desktop
> workload, stats show:
>  - ~80% of pages compressing to PAGE_SIZE/2 or less.
>  - ~1% incompressible pages.
>
>
> For the speed part, please refer to performance numbers at link above.
> It show cases where it help or hurts the performance.
>

Thanks, I'll take a look at the links

-- 
	Balbir
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