linux-kernel - RE: [PATCH v2 0/3] staging: zcache: xcfmalloc support

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Date:	Thu, 15 Sep 2011 15:27:07 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	Nitin Gupta <ngupta@...are.org>, Greg KH <greg@...ah.com>,
	gregkh@...e.de, devel@...verdev.osuosl.org,
	cascardo@...oscopio.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, brking@...ux.vnet.ibm.com,
	rcj@...ux.vnet.ibm.com
Subject: RE: [PATCH v2 0/3] staging: zcache: xcfmalloc support

> From: Dave Hansen [mailto:dave@...ux.vnet.ibm.com]
> Subject: Re: [PATCH v2 0/3] staging: zcache: xcfmalloc support
> 
> On Thu, 2011-09-15 at 14:24 -0500, Seth Jennings wrote:
> > How would you suggest that I measure xcfmalloc performance on a "very
> > large set of workloads".  I guess another form of that question is: How
> > did xvmalloc do this?
> 
> Well, it didn't have a competitor, so this probably wasn't done. :)
> 
> I'd like to see a microbenchmarky sort of thing.  Do a million (or 100
> million, whatever) allocations, and time it for both allocators doing
> the same thing.  You just need to do the *same* allocations for both.

One suggestion:  We already know xvmalloc sucks IF the workload has
poor compression for most pages.  We are looking to understand if xcfmalloc
is [very**N] bad when xvmalloc is good.  So please measure BIG-NUMBER
allocations where compression is known to be OK on average (which is,
I think, a large fraction of workloads), rather than workloads where
xvmalloc already sucks.
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