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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: Linux 2.6.29
Date: Fri, 3 Apr 2009 16:05:20 +1100
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Cc: Jeff Garzik <jeff@garzik.org>, Andrew Morton <akpm@linux-foundation.org>,
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       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Friday 03 April 2009 13:16:08 Linus Torvalds wrote:
> 
> On Thu, 2 Apr 2009, Jeff Garzik wrote:
> > 
> > The most interesting thing I found:  the SSD does 80 MB/s for the first ~1 GB
> > or so, then slows down dramatically.  After ~2GB, it is down to 32 MB/s.
> > After ~4GB, it reaches a steady speed around 23 MB/s.
> 
> Are you sure that isn't an effect of double and triple indirect blocks 
> etc? The metadata updates get more complex for the deeper indirect blocks.
> 
> Or just our page cache lookup? Maybe our radix tree thing hits something 
> stupid. Although it sure shouldn't be _that_ noticeable.

Hmm, I don't know what you have in mind. page cache lookup should be
several orders of magnitude faster than a disk can write the pages out?

Dirty/writeout/clean cycle still has to lock the radix tree to change
tags, but that's really not going to be significantly contended (nor
does it synchronise with simple lookups).
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