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 EFE70C433E0 for ; Thu, 11 Mar 2021 18:58:27 +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 5862C64FAF for ; Thu, 11 Mar 2021 18:58:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5862C64FAF 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]:39342 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lKQVu-0003cQ-8d for qemu-devel@archiver.kernel.org; Thu, 11 Mar 2021 13:58:26 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:33572) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lKQQS-0006BP-MU for qemu-devel@nongnu.org; Thu, 11 Mar 2021 13:52:48 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:55423) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lKQQL-0000Py-Lf for qemu-devel@nongnu.org; Thu, 11 Mar 2021 13:52:47 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615488759; 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=t/Ua4EX5DV5NRY6Lr7zTw+lomYG0jfFKC9Iqa2m00KE=; b=i4zc6eK40M+ahXcg+DLlEWL3gc83IkDDCcea8cA3hXArolHDZOn0taEuBVDhHLz8fCAby9 kIb32w/DZx+5vKe0vhHr16IDulNOvXOsMEVuq9rnwRMX8yhdJHd86QgQWCn2VpjVxvpM4S /tSgsDaNK8/2m/TxxDgcsxGxdLwlJWE= 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-170-9YXYZ0PGPumgtHWHKcZqMg-1; Thu, 11 Mar 2021 13:52:37 -0500 X-MC-Unique: 9YXYZ0PGPumgtHWHKcZqMg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 00621800D55; Thu, 11 Mar 2021 18:52:37 +0000 (UTC) Received: from work-vm (ovpn-115-29.ams2.redhat.com [10.36.115.29]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B9D2F102AE7E; Thu, 11 Mar 2021 18:52:20 +0000 (UTC) Date: Thu, 11 Mar 2021 18:52:17 +0000 From: "Dr. David Alan Gilbert" To: Vivek Goyal 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> <20210311135050.GA145441@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210311135050.GA145441@redhat.com> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.25, 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, Chirantan Ekbote , qemu-devel@nongnu.org, virtio-fs-list , Stefan Hajnoczi , marcandre.lureau@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Vivek Goyal (vgoyal@redhat.com) wrote: > On Thu, Mar 11, 2021 at 12:15:09PM +0000, Dr. David Alan Gilbert wrote: > > * 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? 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. > > > > So this has come out as: > > > > typedef struct { > > /* Offsets within the file being mapped */ > > uint64_t fd_offset; > > /* Offsets within the cache */ > > uint64_t c_offset; > > /* Lengths of sections */ > > uint64_t len; > > /* Flags, from VHOST_USER_FS_FLAG_* */ > > uint64_t flags; > > } VhostUserFSSlaveMsgEntry; > > > > typedef struct { > > /* Generic flags for the overall message */ > > uint32_t flags; > > /* Number of entries */ > > uint16_t count; > > /* Spare */ > > uint16_t align; > > > > VhostUserFSSlaveMsgEntry entries[]; > > } VhostUserFSSlaveMsg; > > > > which seems to work OK. > > I've still got a: > > #define VHOST_USER_FS_SLAVE_MAX_ENTRIES 8 > > Hi Dave, > > So if we were to raise this limit down the line, will it be just a matter > of changing this numebr and recompile qemu + virtiofsd? Or this is just > a limit on sender and qemu does not care. They have to agree; > If qemu cares about number of entries, then it will be good to raise this > limit to say 32 or 64. I've bumped it to 32. Dave > Otherwise new definitions look good. > > Thanks > Vivek > > > > > to limit the size VhostUserFSSlaveMsg can get to. > > The variable length array makes the union in the reader a bit more > > hairy, but it's OK. > > > > 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 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK