From owner-svn-src-head@FreeBSD.ORG Wed Jun 2 06:27:19 2010 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id A4B8B106566C; Wed, 2 Jun 2010 06:27:19 +0000 (UTC) (envelope-from alc@cs.rice.edu) Received: from mail.cs.rice.edu (mail.cs.rice.edu [128.42.1.31]) by mx1.freebsd.org (Postfix) with ESMTP id 686C78FC14; Wed, 2 Jun 2010 06:27:19 +0000 (UTC) Received: from mail.cs.rice.edu (localhost.localdomain [127.0.0.1]) by mail.cs.rice.edu (Postfix) with ESMTP id DB81D2C2C55; Wed, 2 Jun 2010 01:27:18 -0500 (CDT) X-Virus-Scanned: by amavis-2.4.0 at mail.cs.rice.edu Received: from mail.cs.rice.edu ([127.0.0.1]) by mail.cs.rice.edu (mail.cs.rice.edu [127.0.0.1]) (amavisd-new, port 10024) with LMTP id lKJ66GbA3SMz; Wed, 2 Jun 2010 01:27:11 -0500 (CDT) Received: from adsl-216-63-78-18.dsl.hstntx.swbell.net (adsl-216-63-78-18.dsl.hstntx.swbell.net [216.63.78.18]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.cs.rice.edu (Postfix) with ESMTP id 263E52C2B02; Wed, 2 Jun 2010 01:27:09 -0500 (CDT) Message-ID: <4C05F9BC.40409@cs.rice.edu> Date: Wed, 02 Jun 2010 01:27:08 -0500 From: Alan Cox User-Agent: Thunderbird 2.0.0.24 (X11/20100501) MIME-Version: 1.0 To: "C. Jayachandran" References: <201005271005.o4RA5eVu032269@svn.freebsd.org> <4C058145.3000707@cs.rice.edu> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "Jayachandran C." , svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Randall Stewart Subject: Re: svn commit: r208589 - head/sys/mips/mips X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 02 Jun 2010 06:27:19 -0000 C. Jayachandran wrote: > On Wed, Jun 2, 2010 at 3:23 AM, Alan Cox wrote: > >> On 5/27/2010 5:05 AM, Jayachandran C. wrote: >> >>> Author: jchandra >>> Date: Thu May 27 10:05:40 2010 >>> New Revision: 208589 >>> URL: http://svn.freebsd.org/changeset/base/208589 >>> >>> Log: >>> Call VM_WAIT in pmap_ptpgzone_allocf() if M_WAITOK is set. >>> Removed unused variable. >>> >>> Approved by: rrs (mentor) >>> >>> >>> >> I'm afraid that this will work some of the time, but not all of the time. >> Specifically, there is no guarantee that any of the available free (or >> cached) pages after the VM_WAIT will fall within the range of suitable >> physical addresses. Moreover, and perhaps most worrisome, is that this >> function could do a lot of spinning. Every time this function sleeps and a >> single page is freed (or cached) by someone else, this function will be >> reawakened. With a little bad luck, you could spin indefinitely. >> >> For essentially this reason, contigmalloc(), kmem_alloc_contig(), and >> kmem_alloc_attr() don't use VM_WAIT, but instead a function called >> vm_contig_grow_cache(). >> > > I had seen the vm_contig_grow_cache() usage, but could not use it as > it was defined as a static function. > > I did not want to use contigmalloc()/kmem_alloc_contig() either, > because the pages in that memory region are already direct mapped and > setting up another mapping is not necessary. The overall idea is to > allocate pages in the direct mapped region for the page table entries > so that we don't take a TLB exception while accessing page tables > (which is costly as MIPS has a software TLB exception handler). > > Can you suggest the right way to do this? I will make the changes and > send a patch for approval. > I would encourage you to make vm_contig_grow_cache() an extern function and use it. (vm/vm_pageout.h is probably the best place for the function prototype.) If you're interested in taking this a small step further, it would make sense to add two parameters to vm_contig_grow_cache() and vm_contig_launder(): a "low" and a "high" physical address. vm_contig_launder() could then skip pages that are outside the desired range. Regards, Alan