Re: [PATCH] Fixed a mismatch between the users of radix_tree and the implementation.

[Peter Zijlstra <peterz@infradead.org>]

(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@infradead.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