linux-kernel - Re: [PATCH] Fixed a mismatch between the users of radix

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Date:	Mon, 16 Aug 2010 23:06:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Salman Qazi <sqazi@...gle.com>
Cc:	paulmck@...ibm.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, adurbin@...gle.com
Subject: Re: [PATCH] Fixed a mismatch between the users of radix_tree and
 the implementation.

(html damaged email alert)

On Mon, 2010-08-16 at 13:59 -0700, Salman Qazi wrote:
> On Mon, Aug 16, 2010 at 12:33 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>         On Mon, 2010-08-16 at 11:30 -0700, Salman Qazi wrote:
>         > For the delete case,
>         > we no longer shrink the tree back to being just the root containing the
>         > only remaining object.  For the insert case, we no longer store the
>         > first object in the root, rather allocating a node structure for it.  The
>         > reason that this works is that deleting (or inserting) intermediate nodes
>         > does not make a difference to a reader holding a slot.
>         
>         
>         Ah, I through that was what it did. So you basically increase the memory
>         footprint for tiny files.. have you done any measurements on that?
> 

> You raise a valid concern.  I haven't.  What would you recommend as a
> benchmark/metric to measure this?

One thing you could try is something like the below on a freshly booted
machine, once without and once with the patch:

 cd /usr/src/linux-2.6
 echo 1 > /proc/sys/vm/drop_caches
 grep radix /proc/slabinfo
 make bzImage
 echo 1 > /proc/sys/vm/drop_caches
 grep radix /proc/slabinfo



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