linux-kernel - Re: [RFC PATCH 00/12] x86/mm: Implement lockless pgd_alloc()/pgd

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Message-ID: <5579BB76.1020508@zytor.com>
Date:	Thu, 11 Jun 2015 09:46:46 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
CC:	linux-mml@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Waiman Long <Waiman.Long@...com>
Subject: Re: [RFC PATCH 00/12] x86/mm: Implement lockless pgd_alloc()/pgd_free()

On 06/11/2015 07:07 AM, Ingo Molnar wrote:
> Waiman Long reported 'pgd_lock' contention on high CPU count systems and proposed
> moving pgd_lock on a separate cacheline to eliminate false sharing and to reduce
> some of the lock bouncing overhead.
>
> I think we can do much better: this series eliminates the pgd_list and makes
> pgd_alloc()/pgd_free() lockless.

This ties into a slightly different issue, which is how to deal 
*properly* with "special" PGDs like the 1:1 trampoline and the UEFI page 
tables.  These, too, should be able to incorporate, possibly more than 
once, page tables further down.

	-hpa

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