Date: Wed, 3 Sep 2008 15:39:55 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Igor Sysoev <is@rambler-co.ru> Cc: Tor Egge <tegge@freebsd.org>, freebsd-stable@freebsd.org Subject: Re: vfs.ffs.rawreadahead Message-ID: <20080903123955.GE2038@deviant.kiev.zoral.com.ua> In-Reply-To: <20080903095352.GA62541@rambler-co.ru> References: <20080903095352.GA62541@rambler-co.ru>
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--iHi2w+J2QYXBOoee Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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 ? 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. 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. --iHi2w+J2QYXBOoee Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAki+hZoACgkQC3+MBN1Mb4iUzwCeK6uS/EA1LU6Pb9cLEE+L/e16 TawAoMnUlFdZUm11S2ApwjBVO9SToWoW =zxas -----END PGP SIGNATURE----- --iHi2w+J2QYXBOoee--
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