Re: [PATCH] Fixed a mismatch between the users of radix_tree and the implementation.
From: Salman Qazi
Date: Tue Aug 17 2010 - 00:35:37 EST
On Mon, Aug 16, 2010 at 2:06 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> (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@xxxxxxxxxxxxx> 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
>
>
>
>
Here's what I see:
Without the patch:
Before:
radix_tree_node 468 1400 568 28 4 : tunables 0 0
0 : slabdata 50 50 0
After:
radix_tree_node 1886 3192 568 28 4 : tunables 0 0
0 : slabdata 114 114 0
With the patch:
Before:
radix_tree_node 495 1176 568 28 4 : tunables 0 0
0 : slabdata 42 42 0
After:
radix_tree_node 3173 7336 568 28 4 : tunables 0 0
0 : slabdata 262 262 0
So, not particularly good news :(.
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