From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CAFF0C2D0A3 for ; Mon, 9 Nov 2020 17:22:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F29020789 for ; Mon, 9 Nov 2020 17:22:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="HZoJ9FbO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730156AbgKIRWK (ORCPT ); Mon, 9 Nov 2020 12:22:10 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:39506 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730315AbgKIRWJ (ORCPT ); Mon, 9 Nov 2020 12:22:09 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604942527; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=iPzA+EhnV77h5bZsfMW1LPYR+XlARUhnSyNaT1m+xOo=; b=HZoJ9FbOzBvTSY73htM3bsEVXty2Vf472k+YPC2f7koqiN7jcJakKh28rcC89Cy96WgR3b rO/Oh6a79ckgZst2oWPkz33hOa6qDLCeXybS8Azm2lSboZzVnAksBQen1hStUuzostXWG0 u+q4tB4AtRK7lQBLbYUP6El2spqqbAY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-61-njHNrcxSMo2d3zpyim0DIQ-1; Mon, 09 Nov 2020 12:22:06 -0500 X-MC-Unique: njHNrcxSMo2d3zpyim0DIQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BC322800688; Mon, 9 Nov 2020 17:22:04 +0000 (UTC) Received: from horse.redhat.com (ovpn-115-201.rdu2.redhat.com [10.10.115.201]) by smtp.corp.redhat.com (Postfix) with ESMTP id 847CE60C84; Mon, 9 Nov 2020 17:22:04 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id E8954222E35; Mon, 9 Nov 2020 12:22:03 -0500 (EST) Date: Mon, 9 Nov 2020 12:22:03 -0500 From: Vivek Goyal To: Amir Goldstein Cc: Sargun Dhillon , overlayfs , Miklos Szeredi , Giuseppe Scrivano , Daniel J Walsh Subject: Re: [PATCH v7] overlayfs: Provide a mount option "volatile" to skip sync Message-ID: <20201109172203.GF1479853@redhat.com> References: <20200831181529.GA1193654@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org On Fri, Nov 06, 2020 at 09:00:07PM +0200, Amir Goldstein wrote: > On Fri, Nov 6, 2020 at 7:59 PM Sargun Dhillon wrote: > > > > On Mon, Aug 31, 2020 at 11:15 AM Vivek Goyal wrote: > > > > > > Container folks are complaining that dnf/yum issues too many sync while > > > installing packages and this slows down the image build. Build > > > requirement is such that they don't care if a node goes down while > > > build was still going on. In that case, they will simply throw away > > > unfinished layer and start new build. So they don't care about syncing > > > intermediate state to the disk and hence don't want to pay the price > > > associated with sync. > > > > > > So they are asking for mount options where they can disable sync on overlay > > > mount point. > > > > > > They primarily seem to have two use cases. > > > > > > - For building images, they will mount overlay with nosync and then sync > > > upper layer after unmounting overlay and reuse upper as lower for next > > > layer. > > > > > > - For running containers, they don't seem to care about syncing upper > > > layer because if node goes down, they will simply throw away upper > > > layer and create a fresh one. > > > > > > So this patch provides a mount option "volatile" which disables all forms > > > of sync. Now it is caller's responsibility to throw away upper if > > > system crashes or shuts down and start fresh. > > > > > > With "volatile", I am seeing roughly 20% speed up in my VM where I am just > > > installing emacs in an image. Installation time drops from 31 seconds to > > > 25 seconds when nosync option is used. This is for the case of building on top > > > of an image where all packages are already cached. That way I take > > > out the network operations latency out of the measurement. > > > > > > Giuseppe is also looking to cut down on number of iops done on the > > > disk. He is complaining that often in cloud their VMs are throttled > > > if they cross the limit. This option can help them where they reduce > > > number of iops (by cutting down on frequent sync and writebacks). > > > > [...] > > There is some slightly confusing behaviour here [I realize this > > behaviour is as intended]: > > > > (root) ~ # mount -t overlay -o > > volatile,index=off,lowerdir=/root/lowerdir,upperdir=/root/upperdir,workdir=/root/workdir > > none /mnt/foo > > (root) ~ # umount /mnt/foo > > (root) ~ # mount -t overlay -o > > volatile,index=off,lowerdir=/root/lowerdir,upperdir=/root/upperdir,workdir=/root/workdir > > none /mnt/foo > > mount: /mnt/foo: wrong fs type, bad option, bad superblock on none, > > missing codepage or helper program, or other error. > > > > From my understanding, the dirty flag should only be a problem if the > > existing overlayfs is unmounted uncleanly. Docker does > > this (mount, and re-mounts) during startup time because it writes some > > files to the overlayfs. I think that we should harden > > the volatile check slightly, and make it so that within the same boot, > > it's not a problem, and having to have the user clear > > the workdir every time is a pain. In addition, the semantics of the > > volatile patch itself do not appear to be such that they > > would break mounts during the same boot / mount of upperdir -- as > > overlayfs does not defer any writes in itself, and it's > > only that it's short-circuiting writes to the upperdir. > > > > Amir, > > What do you think? > > How do you propose to check that upperdir was used during the same boot? Can we read and store "/proc/sys/kernel/random/boot_id". I am assuming this will change if system is rebooting after a shutdown/reboot/crash. If boot_id has not changed, we can allow remount and delete incomapt dir ourseleves. May be we can drop a file in incomat to store boot_id at the time of overlay mount. Thanks Vivek