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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 C48EAC282DD for ; Fri, 10 Jan 2020 15:51:16 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9125C205F4 for ; Fri, 10 Jan 2020 15:51:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ERnsE6z8" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9125C205F4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48302 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ipwZ9-00075R-Co for qemu-devel@archiver.kernel.org; Fri, 10 Jan 2020 10:51:15 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:56459) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ipwQF-0003jD-AK for qemu-devel@nongnu.org; Fri, 10 Jan 2020 10:42:04 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ipwQD-0003Ll-UJ for qemu-devel@nongnu.org; Fri, 10 Jan 2020 10:42:03 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:58499 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ipwQD-0003Iu-Ph for qemu-devel@nongnu.org; Fri, 10 Jan 2020 10:42:01 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578670921; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=jBg45+LpjtXGUrIhyGhSEWIbaLqX0f99qskaxLuoAWc=; b=ERnsE6z83ep8w3C0/peWwqkhntr1PuE9853tasadpqf11JQPWmjLwXAG2lf01zeiI2tqSD jSqR82aT8wXGYAc/4mncj84xUO08qDQ7VdKa2heZWE69NRMCaRkZDzb5wVL8U8Y4CWys5J KgGWz2c3DDdyf2l/VayPqyGds5Pt2kI= 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-15-aR4sCtifPc-CNSLnxDV7EA-1; Fri, 10 Jan 2020 10:40:42 -0500 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 2D4C8B20E1 for ; Fri, 10 Jan 2020 15:40:41 +0000 (UTC) Received: from horse.redhat.com (unknown [10.18.25.35]) by smtp.corp.redhat.com (Postfix) with ESMTP id 61D5560CC0; Fri, 10 Jan 2020 15:40:38 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id E8339220A24; Fri, 10 Jan 2020 10:40:37 -0500 (EST) Date: Fri, 10 Jan 2020 10:40:37 -0500 From: Vivek Goyal To: Miklos Szeredi Subject: Re: [PATCH 068/104] virtiofsd: passthrough_ll: control readdirplus Message-ID: <20200110154037.GC28043@redhat.com> References: <20191212163904.159893-1-dgilbert@redhat.com> <20191212163904.159893-69-dgilbert@redhat.com> <20200107112316.GL3368802@redhat.com> <20200110150447.GH3901@work-vm> <20200110151808.GT3423494@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-MC-Unique: aR4sCtifPc-CNSLnxDV7EA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , "Dr. David Alan Gilbert" , Stefan Hajnoczi , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Jan 10, 2020 at 04:30:01PM +0100, Miklos Szeredi wrote: > On Fri, Jan 10, 2020 at 4:18 PM Daniel P. Berrang=E9 wrote: > > > > On Fri, Jan 10, 2020 at 04:13:08PM +0100, Miklos Szeredi wrote: > > > On Fri, Jan 10, 2020 at 4:04 PM Dr. David Alan Gilbert > > > wrote: > > > > > > > > * Daniel P. Berrang=E9 (berrange@redhat.com) wrote: > > > > > On Thu, Dec 12, 2019 at 04:38:28PM +0000, Dr. David Alan Gilbert = (git) wrote: > > > > > > From: Miklos Szeredi > > > > > > > > > > > > > > > > What is readdirplus and what do we need a command line option to > > > > > control it ? What's the user benefit of changing the setting ? > > > > > > > > cc'ing Miklos who understands this better than me. > > > > > > > > My understanding is that readdirplus is a heuristic inherited from = NFS > > > > where when you iterate over the directory you also pick up stat() d= ata > > > > for each entry in the directory. You then cache that stat data > > > > somewhere. > > > > The Plus-ness is that a lot of directory operations involve you sta= ting > > > > each entry (e.g. to figure out if you can access it etc) so rolling= it > > > > into one op avoids the separate stat. The unplus-ness is that it's= an > > > > overhead and I think changes some of the caching behaviour. > > > > > > Yeah, so either may give better performance and it's hard to pick a > > > clear winner. NFS also has an option to control this. > > > > IIUC from the man page, the NFS option for controlling this is a client > > side mount option. This makes sense as only the client really has knowl= edge > > of whether its workload will benefit. > > > > With this in mind, should the readdirplus control for virtio-fs also be= a > > guest mount option instead of a host virtiofsd CLI option ? The guest a= dmin > > seems best placed to know whether their workload will benefit or not. >=20 > Definitely. In fact other options, e.g. ones that control caching, > should probably also be client side (cache=3DXXX, writeback, > timeout=3DXXX, etc). I am not sure about cache options. So if we want to share a directory between multiple guests with stronger coherency (cache=3Dnone), then admin should decide that cache=3Dalways/auto is not supported on this export. Also, how will one client know whether there are other clients same directory with strong coherency requirements and it should use cache=3Dnone instead of cache=3Dalways/auto. Having said that, it also makes sense that client knows its workoad and can decide if cache=3Dauto works best for it and use that instead. May be we need both client and server side options. Client will request certain cache=3Dxxx options and server can deny these if admin decides not to enable that option for that particular mount. For example, if admin decides that we can only support cache=3Dnone on this particular dir due to other guest sharing it, then daemon should be able to deny cache=3Dauto/always requests from client. Thanks Vivek