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Message-ID: <20140422200221.GC2314@mtj.dyndns.org>
Date: Tue, 22 Apr 2014 16:02:21 -0400
From: Tejun Heo <tj@...nel.org>
To: Lai Jiangshan <laijs@...fujitsu.com>
Cc: linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Vladimir Davydov <vdavydov@...allels.com>,
Jiri Kosina <jkosina@...e.cz>,
Jeff Layton <jlayton@...hat.com>,
Andreas Gruenbacher <agruen@...bit.com>,
Stephen Hemminger <stephen@...workplumber.org>,
Jean Delvare <jdelvare@...e.de>,
Monam Agarwal <monamagarwal123@...il.com>
Subject: Re: [PATCH 3/4] ida: in-place ida allocation
On Tue, Apr 22, 2014 at 06:16:20PM +0800, Lai Jiangshan wrote:
> There are two stages of ida allocation/free, idr_layers and ida_bitmap.
> They add unneeded foot print and memory waste.
>
> When a single ID is first allocated from an ida, this ida requires
> two big chunks of memory. One idr_layer and one ida_bitmap.
>
> To reduce the foot print and memory, we reduce the ida_bitmap
> to a single "unsigned long" and place it in its own idr-slot
> and avoid to allocate the ida_bitmap.
>
> It also means ida bitmap is located on its coresponding idr-slot
> which size is the same as "unsigned long".
> Each ida bitmap(idr-slot) contains BITS_PER_LONG ida-slots.
>
> The struct ida_bitmap is not needed any more, we use "unsigned long"
> directly and remove all the code of alloc/free struct ida_bitmap.
Are you calling 128 byte a "big chunk of memory" while trading off
tree depth for it? No, this level of space optimizaiton is completely
uncalled for.
Nacked-by: Tejun Heo <tj@...nel.org>
Thanks.
--
tejun
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