From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailgw-01.dd24.net ([193.46.215.41]:57819 "EHLO mailgw-01.dd24.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753607AbbLNXZJ (ORCPT ); Mon, 14 Dec 2015 18:25:09 -0500 Message-ID: <1450135505.6629.66.camel@scientia.net> Subject: Re: btrfs: poor performance on deleting many large files From: Christoph Anton Mitterer To: Lionel Bouton , linux-btrfs@vger.kernel.org Date: Tue, 15 Dec 2015 00:25:05 +0100 In-Reply-To: <566F34F0.8050407@bouton.name> References: <1448488198.4717.4.camel@gmail.com> <1448562347.8809.16.camel@scientia.net> <1448582805.11377.9.camel@scientia.net> <1448683025.6837.4.camel@scientia.net> <1449958538.15961.3.camel@scientia.net> <566ED124.30803@gmail.com> <1450121957.6629.41.camel@scientia.net> <566F261F.4040705@gmail.com> <566F34F0.8050407@bouton.name> Content-Type: multipart/signed; micalg="sha-512"; protocol="application/x-pkcs7-signature"; boundary="=-gFY4ZyFyHJ8urWfjPpFp" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: --=-gFY4ZyFyHJ8urWfjPpFp Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2015-12-14 at 22:30 +0100, Lionel Bouton wrote: > Mutt is often used as an example but tmpwatch uses atime by default > too > and it's quite useful. Hmm one could probably argue that these few cases justify the use of separate filesystems (or btrfs subvols ;) ), so that the majority could benefit of noatime. > If you have a local cache of remote files for which you want a good > hit > ratio and don't care too much about its exact size (you should have > Nagios/Zabbix/... alerting you when a filesystem reaches a %free > limit > if you value your system's availability anyway), using tmpwatch with > cron to maintain it is only one single line away and does the job. > For > an example of this particular case, on Gentoo the > /usr/portage/distfiles > directory is used in one of the tasks you can uncomment to activate > in > the cron.daily file provided when installing tmpwatch. > Using tmpwatch/cron is far more convenient than using a dedicated > cache > (which might get tricky if the remote isn't HTTP-based, like an > rsync/ftp/nfs/... server or doesn't support HTTP IMS requests for > example). > Some http frameworks put sessions in /tmp: in this case if you want > sessions to expire based on usage and not creation time, using > tmpwatch > or similar with atime is the only way to clean these files. This can > even become a performance requirement: I've seen some servers slowing > down with tens/hundreds of thousands of session files in /tmp because > it > was only cleaned at boot and the systems were almost never > rebooted... Okay there are probably some usecases, ... the session cleaning I'd however rather consider a bug in the respective software, especially if it really depends on it to expire the session (what if for some reason tmpwatch get's broken, uninstalled, etc.) > I use noatime and nodiratime FYI: noatime implies nodiratime :-) > Finally Linus Torvalds has been quite vocal and consistent on the > general subject of the kernel not breaking user-space APIs no matter > what so I wouldn't have much hope for default kernel mount options > changes... He surely is right in general,... but when the point has been reached, where only a minority actually requires the feature... and the minority actually starts to suffer from that... it may change. 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