linux-kernel - Re: [PATCH 6/8] idr: avoid ping-pong

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Date:	Fri, 18 Apr 2014 13:17:17 -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>,
	Jean Delvare <jdelvare@...e.de>,
	Monam Agarwal <monamagarwal123@...il.com>,
	Jeff Layton <jlayton@...hat.com>,
	Andreas Gruenbacher <agruen@...bit.com>,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH 6/8] idr: avoid ping-pong

On Fri, Apr 18, 2014 at 08:49:53PM +0800, Lai Jiangshan wrote:
> The ida callers always calls ida_pre_get() before ida_get_new*().
> ida_pre_get() will do layer allocation, and ida_get_new*() will do layer removal.
> 
> It causes an unneeded ping-pong. The speculative layer removal in
> ida_get_new*() can't result expected optimization.
> 
> So we remove the unneeded layer removal in ida_get_new*().

But the as comment says, ida doesn't want to keep extra layers around
as it wants to keep its memory footprint minimal.  I think the right
thing to do is implementing ida_preload() which is simliar to
idr_preload() and do away with per-ida layer cache.

Thanks.

-- 
tejun
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