linux-kernel - Re: [PATCH 2/5] mm: frontswap: lazy initialization to allow tmem backends to build/run as modules

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Date:	Wed, 31 Oct 2012 19:42:53 -0200
From:	Cesar Eduardo Barros <cesarb@...arb.net>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
CC:	Dan Magenheimer <dan.magenheimer@...cle.com>,
	devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, linux-mm@...ck.org, ngupta@...are.org,
	konrad.wilk@...cle.com, minchan@...nel.org, fschmaus@...il.com,
	andor.daam@...glemail.com, ilendir@...glemail.com,
	akpm@...ux-foundation.org, mgorman@...e.de
Subject: Re: [PATCH 2/5] mm: frontswap: lazy initialization to allow tmem
 backends to build/run as modules

Em 31-10-2012 15:05, Seth Jennings escreveu:
> On 10/31/2012 10:07 AM, Dan Magenheimer wrote:
>> +#define MAX_INITIALIZABLE_SD 32
>
> MAX_INITIALIZABLE_SD should just be MAX_SWAPFILES
>
>> +static int sds[MAX_INITIALIZABLE_SD];
>
> Rather than store and array of enabled types indexed by type, why not
> an array of booleans indexed by type.  Or a bitfield if you really
> want to save space.

Since it is indexed by swap_info_struct's type, and frontswap already 
pokes directly inside the swap_info_structs, it would be even cleaner to 
use a boolean field within the swap_info_struct.

And if you are using a field within the swap_info_struct, you could 
overload the already existing frontswap_map field, which should only 
have any use if you have a frontswap module already loaded. That is, 
move the vzalloc of the frontswap_map to within frontswap's init 
function, and call it outside the swapfile_lock/swapon_mutex. This also 
has the advantage of not allocating the frontswap_map when it is not 
going to be used.

-- 
Cesar Eduardo Barros
cesarb@...arb.net
cesar.barros@...il.com
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