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Date:	Thu, 27 Sep 2007 14:54:30 -0400
From:	Hideo AOKI <>
To:	Andi Kleen <>
CC:	Satoshi OSHIMA <>,,
Subject: Re: [RFC/PATCH 2/3] UDP memory usage accounting: accounting unit
 and variable


I apologize for not replying sooner.

Andi Kleen wrote:
> Satoshi OSHIMA <> writes:
>> This patch introduces global variable for UDP memory accounting.
>> The unit is page.
> The global variable doesn't seem to be very MP scalable, especially
> if you change it for each packet. This will be a very hot cache line,
> in the worst case bouncing around a large machine.
> Possible alternatives:
> - Per CPU variables
> - You only change the global on socket creation time (by pre allocating a large
> amount) or when the system comes under memory pressure.
> - Batching of the global updates for multiple packets [that's a variant
> of the previous one, might be still too costly though]
> Also for such variables it's usually good to cache line pad them on SMP
> to avoid false sharing with something else.
> -Andi

Thank you so much for your suggestions.

The implementation of the patch basically followed implementation of
tcp_memory_allocated. However, I should agree that the patch introduces
atomic operations too much. Then, I'll try to use the batching to reduce
the number of atomic operations.

Best regards,
Hideo Aoki

Hitachi Computer Products (America) Inc.
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