From owner-freebsd-stable@FreeBSD.ORG Wed Sep 3 13:01:57 2008 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 969281065678; Wed, 3 Sep 2008 13:01:57 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from mail.terabit.net.ua (mail.terabit.net.ua [195.137.202.147]) by mx1.freebsd.org (Postfix) with ESMTP id 340B18FC08; Wed, 3 Sep 2008 13:01:57 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from skuns.zoral.com.ua ([91.193.166.194] helo=mail.zoral.com.ua) by mail.terabit.net.ua with esmtp (Exim 4.63 (FreeBSD)) (envelope-from ) id 1Karzf-000LT2-NV; Wed, 03 Sep 2008 16:01:55 +0300 Received: from deviant.kiev.zoral.com.ua (root@deviant.kiev.zoral.com.ua [10.1.1.148]) by mail.zoral.com.ua (8.14.2/8.14.2) with ESMTP id m83D1nqG034521 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 3 Sep 2008 16:01:50 +0300 (EEST) (envelope-from kostikbel@gmail.com) Received: from deviant.kiev.zoral.com.ua (kostik@localhost [127.0.0.1]) by deviant.kiev.zoral.com.ua (8.14.2/8.14.2) with ESMTP id m83D1npl015532; Wed, 3 Sep 2008 16:01:49 +0300 (EEST) (envelope-from kostikbel@gmail.com) Received: (from kostik@localhost) by deviant.kiev.zoral.com.ua (8.14.2/8.14.2/Submit) id m83D1nEk015530; Wed, 3 Sep 2008 16:01:49 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: deviant.kiev.zoral.com.ua: kostik set sender to kostikbel@gmail.com using -f Date: Wed, 3 Sep 2008 16:01:49 +0300 From: Kostik Belousov To: Igor Sysoev Message-ID: <20080903130149.GF2038@deviant.kiev.zoral.com.ua> References: <20080903095352.GA62541@rambler-co.ru> <20080903123955.GE2038@deviant.kiev.zoral.com.ua> <20080903124733.GH62541@rambler-co.ru> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="WCiRD21tF6xAtlSs" Content-Disposition: inline In-Reply-To: <20080903124733.GH62541@rambler-co.ru> User-Agent: Mutt/1.4.2.3i X-Virus-Scanned: ClamAV version 0.93.3, clamav-milter version 0.93.3 on skuns.kiev.zoral.com.ua X-Virus-Status: Clean X-Spam-Status: No, score=-4.4 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on skuns.kiev.zoral.com.ua X-Virus-Scanned: mail.terabit.net.ua 1Karzf-000LT2-NV 4dcbe21b2a5eb5d858632c8727f78114 X-Terabit: YES Cc: Tor Egge , freebsd-stable@freebsd.org Subject: Re: vfs.ffs.rawreadahead X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 03 Sep 2008 13:01:57 -0000 --WCiRD21tF6xAtlSs Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Sep 03, 2008 at 04:47:33PM +0400, Igor Sysoev wrote: > On Wed, Sep 03, 2008 at 03:39:55PM +0300, Kostik Belousov wrote: >=20 > > On Wed, Sep 03, 2008 at 01:53:52PM +0400, Igor Sysoev wrote: > > > Hi, > > >=20 > > > could anyone tell what does vfs.ffs.rawreadahead enable ? > > > As I understand it's used in DIRECTIO code that allows read data > > > directly to an userland buffer bypassing the buffer cache. > > > What I can not understand where the read ahead data can be placed in ? > >=20 > > The operation of the ffs_rawread is more accurately described as > > bypassing the page cache. It creates the physical buffer that maps > > the user pages. > >=20 > > The readahead is performed only when the supplied user memory region > > is bigger then blocksize. In this case, two reads are performed > > simultaneously, with both buffers mapping consequent blocks from > > user-supplied buffers. The read operation looks like footsteps. >=20 > Nice! >=20 > As I understand the size limit of one read operation is MAXPHYS, which is > equal to 128K due to LBA28 ATA limit. On SCSI, SATA, and LBA48 ATA this l= imit > can be increased. Is it safe ? As I understand, mnt_iosize_max value, that is topped at MAXPHYS, is used to limit the size of the buffer cluster used for clustered reads/writes. This readw clustering sometimes is called readahead too, but it seems to not be directly related to readahead done by ffs_rawread.c. --WCiRD21tF6xAtlSs Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAki+ir0ACgkQC3+MBN1Mb4jP/QCeO//8yFyh+RvU8FfDnrH4MifQ k0YAoJoe4Mge7t3qehJJKqfbPPlqDC0g =MyOq -----END PGP SIGNATURE----- --WCiRD21tF6xAtlSs--