linux-kernel - Re: [PATCH 1/4] staging: zsmalloc: add gfp flags to zs_create

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Date:	Mon, 28 Jan 2013 11:01:28 -0600
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Nitin Gupta <ngupta@...are.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] staging: zsmalloc: add gfp flags to zs_create_pool

On 01/27/2013 09:39 PM, Minchan Kim wrote:
> Hi Seth,
> 
> On Fri, Jan 25, 2013 at 11:46:15AM -0600, Seth Jennings wrote:
>> zs_create_pool() currently takes a gfp flags argument
>> that is used when growing the memory pool.  However
>> it is not used in allocating the metadata for the pool
>> itself.  That is currently hardcoded to GFP_KERNEL.
>>
>> zswap calls zs_create_pool() at swapon time which is done
>> in atomic context, resulting in a "might sleep" warning.
>>
>> This patch changes the meaning of the flags argument in
>> zs_create_pool() to mean the flags for the metadata allocation,
>> and adds a flags argument to zs_malloc that will be used for
>> memory pool growth if required.
> 
> As I mentioned, I'm not strongly against with this patch but it
> should be last resort in case of not being able to address
> frontswap's init routine's dependency with swap_lock.
> 
> I sent a patch and am waiting reply of Konrand or Dan.
> If we can fix frontswap, it would be better rather than
> changing zsmalloc.

I agree that moving the call to frontswap_init() out of the swap_lock
would be a good thing.  However, it doesn't mean that we still
shouldn't allow the users to control the gfp mask for the allocation
done by zs_create_pool(). While moving the frontswap_init() outside
the lock removes the _need_ for this patch, I think that is it good
API design to allow the user to specify the gfp mask.

Seth

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