linux-kernel - Re: [PATCH V4 1/3] x86: Make page cache mode a real type

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Message-ID: <20141029102859.GA11260@gmail.com>
Date:	Wed, 29 Oct 2014 11:28:59 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Juergen Gross <jgross@...e.com>, hpa@...or.com, x86@...nel.org,
	mingo@...hat.com, stefan.bader@...onical.com,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	konrad.wilk@...cle.com, ville.syrjala@...ux.intel.com,
	david.vrabel@...rix.com, jbeulich@...e.com, toshi.kani@...com
Subject: Re: [PATCH V4 1/3] x86: Make page cache mode a real type


* Thomas Gleixner <tglx@...utronix.de> wrote:

> On Mon, 27 Oct 2014, Juergen Gross wrote:
> > At the moment there are a lot of places that handle setting or getting
> > the page cache mode by treating the pgprot bits equal to the cache mode.
> > This is only true because there are a lot of assumptions about the setup
> > of the PAT MSR. Otherwise the cache type needs to get translated into
> > pgprot bits and vice versa.
> > 
> > This patch tries to prepare for that by introducing a separate type
> > for the cache mode and adding functions to translate between those and
> > pgprot values.
> > 
> > To avoid too much performance penalty the translation between cache mode
> > and pgprot values is done via tables which contain the relevant
> > information.  Write-back cache mode is hard-wired to be 0, all other
> > modes are configurable via those tables. For large pages there are
> > translation functions as the PAT bit is located at different positions
> > in the ptes of 4k and large pages.
> 
> I'm fine with the approach itself. Though I wish you had split this
> patch in several sanely to review pieces.
> 
>   - Introduce enums, helper functions etc. which basically reflect
>     the state of today
> 
>   - Change the usage sites to use the enums and helpers
> 
>   - Convert the enum/helper implementation to the new scheme
> 
>   - Split out the printk change
> 
>   ...

That absolutely has to be done, should any of this introduce 
regressions. The diffstat:

 18 files changed, 344 insertions(+), 212 deletions(-)

is _way_ too large.

Thanks,

	Ingo
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