linux-kernel - Re: [PATCH] zsmalloc: use unsigned long instead of void *

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Message-ID: <4FBB97B2.6050408@linux.vnet.ibm.com>
Date:	Tue, 22 May 2012 08:42:10 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.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>
Subject: Re: [PATCH] zsmalloc: use unsigned long instead of void *

On 05/21/2012 09:19 AM, Seth Jennings wrote:

> On 05/20/2012 09:23 PM, Minchan Kim wrote:
> 
>> We should use unsigned long as handle instead of void * to avoid any
>> confusion. Without this, users may just treat zs_malloc return value as
>> a pointer and try to deference it.
> 
> 
> I wouldn't have agreed with you about the need for this change as people
> should understand a void * to be the address of some data with unknown
> structure.
> 
> However, I recently discussed with Dan regarding his RAMster project
> where he assumed that the void * would be an address, and as such,
> 4-byte aligned.  So he has masked two bits into the two LSBs of the
> handle for RAMster, which doesn't work with zsmalloc since the handle is
> not an address.
> 
> So really we do need to convey as explicitly as possible to the user
> that the handle is an _opaque_ value about which no assumption can be made.


Wasn't really clear here.  All that to say, I think we do need this patch.

Thanks,
Seth

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