Message-ID: <5579BB76.1020508@zytor.com>
Date: Thu, 11 Jun 2015 09:46:46 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org
CC: linux-mml@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Denys Vlasenko <dvlasenk@redhat.com>, Brian Gerst <brgerst@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        Waiman Long <Waiman.Long@hp.com>
Subject: Re: [RFC PATCH 00/12] x86/mm: Implement lockless pgd_alloc()/pgd_free()
References: <1434031637-9091-1-git-send-email-mingo@kernel.org>
In-Reply-To: <1434031637-9091-1-git-send-email-mingo@kernel.org>
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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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