From owner-freebsd-arch@FreeBSD.ORG Sat Mar 23 23:45:10 2013 Return-Path: Delivered-To: arch@freebsd.org Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 7B9D3A41 for ; Sat, 23 Mar 2013 23:45:10 +0000 (UTC) (envelope-from alan.l.cox@gmail.com) Received: from mail-ee0-f50.google.com (mail-ee0-f50.google.com [74.125.83.50]) by mx1.freebsd.org (Postfix) with ESMTP id 175D1157 for ; Sat, 23 Mar 2013 23:45:09 +0000 (UTC) Received: by mail-ee0-f50.google.com with SMTP id d4so369131eek.37 for ; Sat, 23 Mar 2013 16:45:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:x-received:reply-to:in-reply-to:references:date :message-id:subject:from:to:cc:content-type; bh=SfigaqGLgyRANrQkgBcOIjDRq3BD2IsexzrNn7+DPYE=; b=GPTLCLCRK2wbJ6+9PkBBhFmfOLoiqdYAbtD25W3o8DC+USqBy/aNVXkW0NturjErwb sY2ki4m6GH/DLA5uzvsDCr5qn1YII8bqaLTrgH5aP3uxDFxyQKZMRrQnvqXnMlvFEJXv rOkwp/bQDRl46I+h17fqk7jq9ih3+juzWygqs5PZWl18oTdkrGfEAgjuSp2SbqCTaxR4 K4HAurQ6Pdh6Ml1UyJ5xTIIPtdNUlxJx9tQXFCHE0DzJiSHx7v0UNlKX/ggK5RCIrJeL bjHQZb2N04bUoiHKg9FisXIUokveY0P5xJfSx2Xy2GCUMMkvBjIxPmkry9/MScANdLwo tuhQ== MIME-Version: 1.0 X-Received: by 10.14.194.198 with SMTP id m46mr18503591een.8.1364082303075; Sat, 23 Mar 2013 16:45:03 -0700 (PDT) Received: by 10.223.127.134 with HTTP; Sat, 23 Mar 2013 16:45:02 -0700 (PDT) In-Reply-To: <20130323221039.GO3794@kib.kiev.ua> References: <20130323211001.GN3794@kib.kiev.ua> <20130323221039.GO3794@kib.kiev.ua> Date: Sat, 23 Mar 2013 18:45:02 -0500 Message-ID: Subject: Re: VM_BCACHE_SIZE_MAX on i386 From: Alan Cox To: Konstantin Belousov Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.14 Cc: arch@freebsd.org, David Wolfskill X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list Reply-To: alc@freebsd.org List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 23 Mar 2013 23:45:10 -0000 On Sat, Mar 23, 2013 at 5:10 PM, Konstantin Belousov wrote: > On Sat, Mar 23, 2013 at 04:49:06PM -0500, Alan Cox wrote: > > The additional KVA that we had to reserve for the vm_page radix tree > nodes > > already got me thinking about VM_BCACHE_SIZE_MAX a couple weeks ago. > With > > the extra KVA pressure that is inherent to PAE, e.g., a larger vm_page > > struct, we really can't afford to allow the buffer map KVA allocation to > > grow much beyond what it would be for a 4GB machine anyway. Moreover, > your > > work makes the size of the buffer map less important, because it will see > > decreasing use as drivers are converted to allow unmapped I/O. So, I > would > > encourage you to simply use the same cap based on a 4 GB machine for both > > PAE and !PAE. > > I did not checked it, but isn't default PAE config splits user/kernel > on the 2GB boundary ? This makes the KVA pressure on PAE less severe, > but user mode should be not very happy. > > No, the PAE split between user/kernel is the same as !PAE. The PAE config is deceptive because it takes twice as many page table pages to get the same 1 GB of KVA. > Currently, the number of the regular buffer headers allocated is equal > to the size of the buffer map / BKVASIZE still. This could be changed > now, I believe that Peter' testing fixed most of the bugs in the > handling of the maxbufspace. I was too coward to make this change > together with the rest of the work. But it could indeed be useful, since > buffer map is used only by the metadata buffers for UFS. > > I did changed VM_BCACHE_SIZE_MAX as you suggested, thanks. > > http://people.freebsd.org/~kib/misc/i386_maxbcache.2.patch >