linux-kernel - Re: [PATCH 1 of 4] mm: add a ptep_modify

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Date:	Thu, 19 Jun 2008 10:57:00 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	benh@...nel.crashing.org
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	xen-devel <xen-devel@...ts.xensource.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Hugh Dickins <hugh@...itas.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1 of 4] mm: add a ptep_modify_prot	transaction	abstraction

Benjamin Herrenschmidt wrote:
>> Which architecture are you interested in?  If it isn't x86, you can 
>> probably get anything past Linus ;)
>>
>> I'll do some measurements to see what effect the batchable 
>> ptep_set_wrprotect() has on native.  If it's significant, I'll propose 
>> making it conditional on CONFIG_PARAVIRT.
>>     
>
> Oh, I mostly think about powerpc, I just wondered if I could re-use
> your new stuff in that context. Mostly idle thoughts at this stage, I
> haven't looked seriously.
>   

There are general-purpose hooks in the common code which architectures 
can implement however they like.  In x86-land we hook them up to pvops, 
but you can handle them however you want.

> I have an old patch set to batch forks (and mprotect etc...) TLB
> invalidations (which is what I really want to batch on powerpc, more
> than the actual PTE changes) that involves subtle changes to the
> batching mechanisms etc...
>   

Do you mean setting up batches of per-page tlb shootdowns rather than 
going a global tlb flush at the end?

    J
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