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=-5.1 required=3.0 tests=BAYES_00,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 D0DD5C433DB for ; Mon, 15 Feb 2021 13:43:41 +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 6B6F464E2C for ; Mon, 15 Feb 2021 13:43:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6B6F464E2C 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]:54418 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lBeA8-0006B5-KH for qemu-devel@archiver.kernel.org; Mon, 15 Feb 2021 08:43:40 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:33776) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lBdsg-0004wD-Vt for qemu-devel@nongnu.org; Mon, 15 Feb 2021 08:25:39 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:26819) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lBdse-0000hm-8T for qemu-devel@nongnu.org; Mon, 15 Feb 2021 08:25:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613395534; 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=Lv0RKSP5jXYchIx+2WPR21e2so+Kcwoj+GlnQBOQc/c=; b=eyS0n7SuwQQoIj5ssImMDXn08DIxcmtsORI2zYkfK2irUiMJfmjHCpZ6FeT94vN0nnYC8O 8o5PYbZ0np3k0qR+eRhrnHFn+HGop4mHlDh7zhXuXgr+ZxDbXNBWk1Hx/RSclo4zO2CDvr t9pR/uSmST/1Ep1G+Q2soQgLcb4fycI= 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-308-NUI6xn0oMXGokHO7gZWc8Q-1; Mon, 15 Feb 2021 08:25:32 -0500 X-MC-Unique: NUI6xn0oMXGokHO7gZWc8Q-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BE645801A93; Mon, 15 Feb 2021 13:25:31 +0000 (UTC) Received: from work-vm (ovpn-115-61.ams2.redhat.com [10.36.115.61]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7AE9D62679; Mon, 15 Feb 2021 13:25:16 +0000 (UTC) Date: Mon, 15 Feb 2021 13:25:13 +0000 From: "Dr. David Alan Gilbert" To: Chirantan Ekbote Subject: Re: [Virtio-fs] [PATCH 07/24] DAX: virtio-fs: Add vhost-user slave commands for mapping Message-ID: References: <20210209190224.62827-1-dgilbert@redhat.com> <20210209190224.62827-8-dgilbert@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: mst@redhat.com, qemu-devel@nongnu.org, virtio-fs-list , Stefan Hajnoczi , marcandre.lureau@redhat.com, Vivek Goyal Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Chirantan Ekbote (chirantan@chromium.org) wrote: > On Wed, Feb 10, 2021 at 4:04 AM Dr. David Alan Gilbert (git) > wrote: > > > > From: "Dr. David Alan Gilbert" > > + > > +typedef struct { > > + /* Offsets within the file being mapped */ > > + uint64_t fd_offset[VHOST_USER_FS_SLAVE_ENTRIES]; > > + /* Offsets within the cache */ > > + uint64_t c_offset[VHOST_USER_FS_SLAVE_ENTRIES]; > > + /* Lengths of sections */ > > + uint64_t len[VHOST_USER_FS_SLAVE_ENTRIES]; > > + /* Flags, from VHOST_USER_FS_FLAG_* */ > > + uint64_t flags[VHOST_USER_FS_SLAVE_ENTRIES]; > > +} VhostUserFSSlaveMsg; > > + > > Is it too late to change this? No; this is a message defined as part of this series so still up for review. It's not guest visible; just on the vhist-user pipe. > This struct allocates space for up to > 8 entries but most of the time the server will only try to set up one > mapping at a time so only 32 out of the 256 bytes in the message are > actually being used. We're just wasting time memcpy'ing bytes that > will never be used. Is there some reason this can't be dynamically > sized? Something like: > > typedef struct { > /* Number of mapping requests */ > uint16_t num_requests; > /* `num_requests` mapping requests */ > MappingRequest requests[]; > } VhostUserFSSlaveMsg; > > typedef struct { > /* Offset within the file being mapped */ > uint64_t fd_offset; > /* Offset within the cache */ > uint64_t c_offset; > /* Length of section */ > uint64_t len; > /* Flags, from VHOST_USER_FS_FLAG_* */ > uint64_t flags; > } MappingRequest; > > The current pre-allocated structure both wastes space when there are > fewer than 8 requests and requires extra messages to be sent when > there are more than 8 requests. I realize that in the grand scheme of > things copying 224 extra bytes is basically not noticeable but it just > irks me that we could fix this really easily before it gets propagated > to too many other places. Sure; I'll have a look. I think at the moment the only more-than-one-entry case is the remove mapping case. Dave > Chirantan > > > -- > > 2.29.2 > > > > _______________________________________________ > > Virtio-fs mailing list > > Virtio-fs@redhat.com > > https://www.redhat.com/mailman/listinfo/virtio-fs > > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK