From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailgw-01.dd24.net ([193.46.215.41]:43691 "EHLO mailgw-01.dd24.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966591AbbLPWO5 (ORCPT ); Wed, 16 Dec 2015 17:14:57 -0500 Message-ID: <1450304093.6242.54.camel@scientia.net> Subject: Re: btrfs: poor performance on deleting many large files From: Christoph Anton Mitterer To: Duncan <1i5t5.duncan@cox.net>, linux-btrfs@vger.kernel.org Date: Wed, 16 Dec 2015 23:14:53 +0100 In-Reply-To: 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> Content-Type: multipart/signed; micalg="sha-512"; protocol="application/x-pkcs7-signature"; boundary="=-eigo91jOwmg3Ah1QV8lY" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: --=-eigo91jOwmg3Ah1QV8lY Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2015-12-13 at 07:10 +0000, Duncan wrote: > > So you basically mean that ro snapshots won't have their atime > > updated > > even without noatime? > > Well I guess that was anyway the recent behaviour of Linux > > filesystems, > > and only very old UNIX systems updated the atime even when the fs > > was > > set ro. >=20 > I'd test it to be sure before relying on it (keeping in mind that my > own=20 > use-case doesn't include subvolumes/snapshots so it's quite possible > I=20 > could get fine details of this nature wrong), but that would be my > very=20 > (_very_! see next) strong assumption, yes. >=20 > Because read-only snapshots are used for btrfs-send among other > things,=20 > with the idea being that the read-only will keep them from changing > in=20 > the middle of the send, and ro snapshot atime updates would seem to > throw=20 > that entirely out the window.=C2=A0=C2=A0So I can't imagine ro snapshots = doing > atime=20 > updates under any circumstance because I just can't see how send > could=20 > rely on them then, but I'd still test it before counting on it. For those who haven't followed up the other threads: I've tried it out and yes, ro-snapshots (as well as ro mounted btrfs filesystem/subvolumes) don't have their atimes changed on e.g. read. > AFAIK, the general idea was to eventually have all the (possible, > some=20 > are global-filesystem-scope) subvolume mount options exposed as=20 > properties, it's just not implemented yet, but I'm not entirely sure > if=20 > that was all /btrfs-specific/ mount options, or included the generic > ones=20 > such as the *atime and no* (noexec/nodev/...) options as well.=C2=A0=C2= =A0In > view=20 > of that and the fact that noatime is generic, adding it as a specific > request still makes sense.=C2=A0=C2=A0Someone with more specific knowledg= e on > the=20 > current plan can remove it if it's already covered. Not sure if I'd had already posted that here, but I did write some of these ideas up and added it to the wiki: https://btrfs.wiki.kernel.org/index.php?title=3DProject_ideas&action=3Dhist= orysubmit&diff=3D29757&oldid=3D29743 Best wishes, Chris. --=-eigo91jOwmg3Ah1QV8lY Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCCEZIw ggW/MIIDp6ADAgECAgMCOakwDQYJKoZIhvcNAQENBQAwVDEUMBIGA1UEChMLQ0FjZXJ0IEluYy4x HjAcBgNVBAsTFWh0dHA6Ly93d3cuQ0FjZXJ0Lm9yZzEcMBoGA1UEAxMTQ0FjZXJ0IENsYXNzIDMg Um9vdDAeFw0xNDA2MTIxNjM2MThaFw0xNjA2MTExNjM2MThaMHwxITAfBgNVBAMTGENocmlzdG9w aCBBbnRvbiBNaXR0ZXJlcjEkMCIGCSqGSIb3DQEJARYVY2FsZXN0eW9Ac2NpZW50aWEubmV0MTEw LwYJKoZIhvcNAQkBFiJtYWlsQGNocmlzdG9waC5hbnRvbi5taXR0ZXJlci5uYW1lMIIBIjANBgkq hkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA4phP/j9vT9dZT+k3ffHxvRWMOuzBnu5O3Fl4y2+WL7pL 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