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

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Date:	Wed, 23 Apr 2014 09:55:49 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
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 04/23/2014 03:58 AM, Tejun Heo wrote:
> 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.

Do you mean "I need additional free layers to
hide any possible bugs"? let me nervous.

> With preloading we aren't even caching it
> per-idr.  I don't think this is something we want to do.

Understood.

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

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