linux-kernel - Re: [PATCH] zsmalloc: Add Kconfig for enabling PTE method

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Date:	Wed, 6 Feb 2013 10:44:04 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zsmalloc: Add Kconfig for enabling PTE method

Hi Greg,

On Tue, Feb 05, 2013 at 05:42:59PM -0800, Greg Kroah-Hartman wrote:
> On Wed, Feb 06, 2013 at 10:17:21AM +0900, Minchan Kim wrote:
> > > > > Did you test this?  I don't see the new config value you added actually
> > > > > do anything in this code.  Also, if I select it incorrectly on ARM, or
> > > > 
> > > > *slaps self*
> > > 
> > > Ok, so I'll drop this patch now.  As for what to do instead, I have no
> > > idea, sorry, but the others should.
> > 
> > Okay. Then, let's discuss further.
> > The history we introuced copy-based method is due to portability casused by
> > set_pte and __flush_tlb_one usage in young zsmalloc age. They are gone now
> > so there isn't issue any more. But we found copy-based method is 3 times faster
> > than pte-based in VM so I expect you guys don't want to give up it for just
> > portability. Of course,
> > I can't give up pte-based model as you know well, it's 6 times faster than
> > copy-based model in ARM.
> > 
> > Hard-coding for some arch like now isn't good and Kconfig for selecting choice
> > was rejected by Greg as you can see above.
> 
> I rejected your patch because it did not do anything, why would I accept
> it?
> 
> What would you have done in my situation?
> 
> It's not an issue of "portability" or "speed" or anything other than
> "the patch you sent was obviously not correct."

I totally misunderstood that you'd like to solve this issue.
"Also, if I select it incorrectly on ARM, or
or other platforms, what is keeping this from doing bad things?"
Then, I will resend it soon.

Thanks.

> 
> greg k-h
> 
> --
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-- 
Kind regards,
Minchan Kim
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