linux-kernel - Re: [PATCH 2/4] idr: reduce the number of MAX_IDR

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Message-ID: <20140422195821.GB2314@mtj.dyndns.org>
Date:	Tue, 22 Apr 2014 15:58:21 -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>,
	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 2/4] idr: reduce the number of MAX_IDR_FREE

On Tue, Apr 22, 2014 at 06:16:19PM +0800, Lai Jiangshan wrote:
> +/*
> + * Number of idr_layer structs to leave in free list.
> + * When idr is not empty, we need atmost (MAX_IDR_LEVEL - 1) idr_layers
> + * to build up and atmost (MAX_IDR_LEVEL - 1) idr_layers to allocate down.
> + * When idr is empty need atmost MAX_IDR_LEVEL layers.
> + */
> +#define MAX_IDR_FREE max((MAX_IDR_LEVEL * 2 - 2), MAX_IDR_LEVEL)

I don't know.  Do we really wanna be this sophiscated about it when
the cost of mistake would be an unexpected id allocation failure which
would *EXTREMELY* difficult to track down or reproduce?  Let's please
keep it dumb and safe.  With preloading we aren't even caching it
per-idr.  I don't think this is something we want to do.

 Nacked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun
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