From owner-svn-src-head@FreeBSD.ORG Thu Jun 3 04:38:07 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 9799F106566C; Thu, 3 Jun 2010 04:38:07 +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 589218FC0A; Thu, 3 Jun 2010 04:38:07 +0000 (UTC) Received: from mail.cs.rice.edu (localhost.localdomain [127.0.0.1]) by mail.cs.rice.edu (Postfix) with ESMTP id 4A9C22C2A8E; Wed, 2 Jun 2010 23:38:06 -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 4cWBr5zj89Rg; Wed, 2 Jun 2010 23:37:58 -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 132042C2A81; Wed, 2 Jun 2010 23:37:58 -0500 (CDT) Message-ID: <4C0731A5.7090301@cs.rice.edu> Date: Wed, 02 Jun 2010 23:37:57 -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> <4C05F9BC.40409@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: Thu, 03 Jun 2010 04:38:07 -0000 C. Jayachandran wrote: > On Wed, Jun 2, 2010 at 11:57 AM, Alan Cox wrote: > >> 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.) >> > > I'll create a patch for this and related changes in mips/mips/pmap.c > > Great. Thanks! >> 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. >> > > I am looking at this now, part of the logic which > vm_phys_alloc_contig() uses to check pages address should work here. > Will send out changes for this, if it works out. > > I suspect that you'll just need to add two or three lines to vm_contig_launder(). If something doesn't make sense, just e-mail me. Regards, Alan