From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from AM1EHSOBE006.bigfish.com (am1ehsobe006.messaging.microsoft.com [213.199.154.209]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (Client CN "mail.global.frontbridge.com", Issuer "Cybertrust SureServer Standard Validation CA" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id 7F280B6FB3 for ; Tue, 24 May 2011 09:31:15 +1000 (EST) Date: Mon, 23 May 2011 18:31:00 -0500 From: Scott Wood To: Benjamin Herrenschmidt Subject: Re: [PATCH 2/7] powerpc/mm: 64-bit 4k: use a PMD-based virtual page table Message-ID: <20110523183100.36c54904@schlenkerla.am.freescale.net> In-Reply-To: <1306183861.7481.208.camel@pasglop> References: <20110518210528.GA29524@schlenkerla.am.freescale.net> <1305754435.7481.3.camel@pasglop> <20110520155719.32e51635@schlenkerla.am.freescale.net> <1305929736.7481.188.camel@pasglop> <20110523135433.557e2d63@schlenkerla.am.freescale.net> <1306183861.7481.208.camel@pasglop> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Cc: linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 24 May 2011 06:51:01 +1000 Benjamin Herrenschmidt wrote: > Is your linear mapping bolted ? If it is you may be able to cut out most > of the save/restore stuff (SRR0,1, ...) since with a normal walk you > won't take nested misses. It is bolted -- we ignore anything we can't map with 16 entries. The only semi-realistic case I can think of where we might bump into that (and thus want non-bolted memory), especially with more than negligible loss compared to the size of memory, is AMP with a non-zero start address where we have to stick with smaller pages due to alignment. Even so, 16 times the alignment of the start of RAM doesn't seem that unreasonable a limit. The 32-bit limit of 3 entries for lowmem is a bit more troublesome there. -Scott