linux-kernel - Re: [PATCH v2] zsmalloc: Add Kconfig for enabling PTE method

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Date:	Thu, 7 Feb 2013 08:16:03 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>
Subject: Re: [PATCH v2] zsmalloc: Add Kconfig for enabling PTE method

On Wed, Feb 06, 2013 at 10:47:16AM -0600, Seth Jennings wrote:
> On 02/05/2013 08:17 PM, Minchan Kim wrote:
> > Zsmalloc has two methods 1) copy-based and 2) pte-based to access
> > allocations that span two pages. You can see history why we supported
> > two approach from [1].
> > 
> > In summary, copy-based method is 3 times fater in x86 while pte-based
> > is 6 times faster in ARM.
> > 
> > But it was bad choice that adding hard coding to select architecture
> > which want to use pte based method. This patch removed it and adds
> > new Kconfig to select the approach.
> > 
> > This patch is based on next-20130205.
> > 
> > [1] https://lkml.org/lkml/2012/7/11/58
> > 
> > * Changelog from v1
> >   * Fix CONFIG_PGTABLE_MAPPING in zsmalloc-main.c - Greg
> > 
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> > Cc: Nitin Gupta <ngupta@...are.org>
> > Cc: Dan Magenheimer <dan.magenheimer@...cle.com>
> > Cc: Konrad Rzeszutek Wilk <konrad@...nok.org>
> > Signed-off-by: Minchan Kim <minchan@...nel.org>
> > ---
> >  drivers/staging/zsmalloc/Kconfig         | 12 ++++++++++++
> >  drivers/staging/zsmalloc/zsmalloc-main.c | 20 +++++---------------
> >  2 files changed, 17 insertions(+), 15 deletions(-)
> > 
> > diff --git a/drivers/staging/zsmalloc/Kconfig b/drivers/staging/zsmalloc/Kconfig
> > index 9084565..232b3b6 100644
> > --- a/drivers/staging/zsmalloc/Kconfig
> > +++ b/drivers/staging/zsmalloc/Kconfig
> > @@ -8,3 +8,15 @@ config ZSMALLOC
> >  	  non-standard allocator interface where a handle, not a pointer, is
> >  	  returned by an alloc().  This handle must be mapped in order to
> >  	  access the allocated space.
> > +
> > +config PGTABLE_MAPPING
> > +        bool "Use page table mapping to access allocations that span two pages"
> > +        depends on ZSMALLOC
> > +        default n
> > +        help
> > +	  By default, zsmalloc uses a copy-based object mapping method to access
> > +	  allocations that span two pages. However, if a particular architecture
> > +	  performs VM mapping faster than copying, then you should select this.
> > +	  This causes zsmalloc to use page table mapping rather than copying
> > +	  for object mapping. You can check speed with zsmalloc benchmark[1].
> > +	  [1] https://github.com/spartacus06/zsmalloc
> 
> Hmm, I'm not sure we want to include this link in the Kconfig.  While  I
> don't have any plans to take that repo down, I could see it getting
> stale at some point for yet-to-be-determined reasons.
> 
> Of course, without this tool (or something like it) it is hard to know
> which option is better for your particular platform.
> 
> Would having this in a Documentation/ file, once one exists, be better?

It could be better. Then, Let's point out that documentataion in Kconfig.
Okay, Let's sort it out.

> 
> Seth
> 
> --
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-- 
Kind regards,
Minchan Kim
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