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 18:05:23 -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 17:52 -0800, Thomas Gleixner wrote:
> On Fri, 12 Mar 2010, Suresh Siddha wrote:
> > 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.
> 
> Care to explain why a rwlock is a good solution and which problem is
> solved by the conversion of a spinlock to a rwlock ?

Thomas, This is the original posting from Robin.

http://marc.info/?l=linux-kernel&m=126720623119649&w=2

lookup_memtype() currently takes the memtype spinlock. Changing this to
a readlock will allow multiple folks to go through this in parallel.

thanks,
suresh

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