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

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Date:	Tue, 22 May 2012 22:55:01 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	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 Wed, May 23, 2012 at 09:02:30AM +0900, Minchan Kim wrote:
> On 05/21/2012 11:19 PM, 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.
> > 
> > Also, I wanted to test this but is doesn't apply cleanly on
> > zsmalloc-main.c on v3.4 or what I have as your latest patch series.
> > What is the base for this patch?
> 
> 
> It's based on next-20120518.
> I have always used linux-next tree for staging.
> Greg, What's the convenient tree for you?

linux-next is fine.

But note, I'm ignoring all patches for the next 2 weeks, especially
staging patches, as this is the merge window time, and I can't apply
anything to my trees, sorry.

After 3.5-rc1 is out, then I will look at new stuff like this again.

thanks,

greg k-h
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