Message-ID: <4FBB97B2.6050408@linux.vnet.ibm.com>
Date: Tue, 22 May 2012 08:42:10 -0500
From: Seth Jennings <sjenning@linux.vnet.ibm.com>
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To: Minchan Kim <minchan@kernel.org>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Dan Magenheimer <dan.magenheimer@oracle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Nitin Gupta <ngupta@vflare.org>
Subject: Re: [PATCH] zsmalloc: use unsigned long instead of void *
References: <1337567013-4741-1-git-send-email-minchan@kernel.org> <4FBA4EE2.8050308@linux.vnet.ibm.com>
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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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