From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from frost.carfax.org.uk ([85.119.82.111]:46804 "EHLO frost.carfax.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753497AbdIDKyp (ORCPT ); Mon, 4 Sep 2017 06:54:45 -0400 Date: Mon, 4 Sep 2017 10:54:44 +0000 From: Hugo Mills To: Marat Khalili Cc: linux-btrfs@vger.kernel.org Subject: Re: Is autodefrag recommended? Message-ID: <20170904105444.GA23980@carfax.org.uk> References: <710ec5d1-adbf-4ce5-50a5-8b8266ccb672@rqc.ru> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="3MwIy2ne0vdjdPXF" In-Reply-To: <710ec5d1-adbf-4ce5-50a5-8b8266ccb672@rqc.ru> Sender: linux-btrfs-owner@vger.kernel.org List-ID: --3MwIy2ne0vdjdPXF Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Mon, Sep 04, 2017 at 12:31:54PM +0300, Marat Khalili wrote: > Hello list, > good time of the day, > > More than once I see mentioned in this list that autodefrag option > solves problems with no apparent drawbacks, but it's not the > default. Can you recommend to just switch it on indiscriminately on > all installations? > > I'm currently on kernel 4.4, can switch to 4.10 if necessary (it's > Ubuntu that gives us this strange choice, no idea why it's not 4.9). > Only spinning rust here, no SSDs. autodefrag effectively works by taking a small region around every write or cluster of writes and making that into a stand-alone extent. This has two consequences: - You end up duplicating more data than is strictly necessary. This is, IIRC, something like 128 KiB for a write. - There's an I/O overhead for enabling autodefrag, because it's increasing the amount of data written. Hugo. -- Hugo Mills | The future isn't what it used to be. hugo@... carfax.org.uk | http://carfax.org.uk/ | PGP: E2AB1DE4 | --3MwIy2ne0vdjdPXF Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJZrTD0AAoJEFheFHXiqx3k6coP/RYnVyUr9t1vpXCXMOM4Lp3j i+g+fVKILq32tEpXRxWXEGj7wCl7W0aFSaI0vWIc1ZGpGOeF9kkJRykfSyRTg/4b tsCa58DEmAdJ3kGxu3hgtQ6SoxT7/z6V2DlWI5VM6EmBYbhnOOCOVeWJNa/kjHpa ejZiqAertS9lHKMcwYvb1+JwpQwwGLPQsQz0sXDcfrovpcSxeXNkNynflB9gkqwg BgTbCqwtQWLsAZ+4oa5fj0ESLkFpKxvG6i2en+56CWJtZ9opgayGl0HswH6c1Vcz A7FVgEMwySeZRqDXE1ev4mjWtXUwwFDiIbg3W5MCBpr0wWQmzeEP0/aTuUEzeIgT 2Vko80O2bFdCYgeHl1D8CYEZ+uN9rWUk/25mRerq49QQSAC0e8pmmcRREueLudlh v4qo63wZedWvxR7pK3/o7alqDAdaYhxGOP29m3hbmQJV7DiqHPFEjB1oYz5d5u3S vCBhY3DnF2VlXBu1Nt3KDo+BR3sczjx4XHKkHO7Dz/5azbLNNmOwgAwE3FX0Ta4Y Bmzc2z7/+J0wSftxF2Uo1c7ZsqyNpATSxiT89f4r9Jskedh3gTl9ysnETIm/FUaB hf2fwCXLahBE+IlzoxEOzaknMdYy5jyWLQlOysAoR0rLVbmOafCcaABVuwADT5yT eA24Dr7iVbRRNLzWJDCc =wbzW -----END PGP SIGNATURE----- --3MwIy2ne0vdjdPXF--