linux-kernel - Re: [Patch] x86,pat Update the page flags for memtype atomically instead of using memtype

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Date:	Fri, 12 Mar 2010 17:46:02 -0800
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Robin Holt <holt@....com>, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [Patch] x86,pat Update the page flags for memtype atomically
 instead of using memtype_lock.

On Fri, 2010-03-12 at 17:08 -0800, Thomas Gleixner wrote:
> On Fri, 12 Mar 2010, Suresh Siddha wrote:
> > On Thu, 2010-03-11 at 08:17 -0800, Robin Holt wrote:
> > > Changes since -V1:
> > > 1) Introduce atomically setting and clearing the page flags and not
> > > using the global memtype_lock to protect page->flags.
> > > 
> > > 2) This allowed me the opportunity to convert the rwlock back into a
> > > spinlock and not affect _MY_ tests performance as all the pages my test
> > > was utilizing are tracked by struct pages.
> > 
> > Can you also include this spinlock to rwlock conversion, which can be
> > used for non RAM pages as a second patch?
> 
> spinlock -> rwlock conversion ? I hope you meant it the other way
> round as Robin said in #2 :)

Thomas, No. I meant converting the existing memtype_lock which is a
spinlock into rwlock. Robin has this in the first version of the patch
but he dropped it in a later version as he avoided this lock for RAM
pages.

Just wanted to make sure that we address the perf aspect even for non
RAM pages by converting the memtype_lock into rwlock before some one
else reports a similar issue for non RAM pages.

thanks,
suresh

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