linux-kernel - Re: [PATCHv4 04/39] radix-tree: implement preload for multiple contiguous elements

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Message-ID: <519CD42C.6040600@sr71.net>
Date:	Wed, 22 May 2013 07:20:28 -0700
From:	Dave Hansen <dave@...1.net>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 04/39] radix-tree: implement preload for multiple contiguous
 elements

On 05/22/2013 05:03 AM, Kirill A. Shutemov wrote:
> On most machines we will have RADIX_TREE_MAP_SHIFT=6. In this case,
> on 64-bit system the per-CPU feature overhead is
>  for preload array:
>    (30 - 21) * sizeof(void*) = 72 bytes
>  plus, if the preload array is full
>    (30 - 21) * sizeof(struct radix_tree_node) = 9 * 560 = 5040 bytes
>  total: 5112 bytes
> 
> on 32-bit system the per-CPU feature overhead is
>  for preload array:
>    (19 - 11) * sizeof(void*) = 32 bytes
>  plus, if the preload array is full
>    (19 - 11) * sizeof(struct radix_tree_node) = 8 * 296 = 2368 bytes
>  total: 2400 bytes
> ---
> 
> Is it good enough?

Yup, just stick the calculations way down in the commit message.  You
can put the description that it "eats about 5k more memory per-cpu than
existing code" up in the very beginning.
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