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[23.128.96.18]) by mx.google.com with ESMTP id w26si2205080eju.654.2020.08.26.12.20.57; Wed, 26 Aug 2020 12:21:20 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=gc9pDjXC; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727910AbgHZTRh (ORCPT + 99 others); Wed, 26 Aug 2020 15:17:37 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:57059 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726988AbgHZTRa (ORCPT ); Wed, 26 Aug 2020 15:17:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1598469447; 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=JwcANZhA8W6K53dylWiceQBVhU3tV8RvSRl3XFIVabA=; b=gc9pDjXClXSuNWCSuZK2KQCmfAyun7G35NgEifGhLQSerwyVN2qn07NPM4ZDZdLGhKPEaf HUACVDU8gs+rxaugyxkShjDBYLYQqIOXfHR7MJjwtHzfz1bx6MxkFYHuH+Nxe+cLYbWdVY janOoxl0p1IEKACc94j8DwGg+ottlfg= 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-141-UyPiH8JVNKCHGWvTJiA_xA-1; Wed, 26 Aug 2020 15:17:23 -0400 X-MC-Unique: UyPiH8JVNKCHGWvTJiA_xA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 21AEE1DDFC; Wed, 26 Aug 2020 19:17:22 +0000 (UTC) Received: from work-vm (ovpn-112-133.ams2.redhat.com [10.36.112.133]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6267618B59; Wed, 26 Aug 2020 19:17:14 +0000 (UTC) Date: Wed, 26 Aug 2020 20:17:11 +0100 From: "Dr. David Alan Gilbert" To: Stefan Hajnoczi Cc: Vivek Goyal , Miklos Szeredi , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm , virtio-fs-list , Dan Williams Subject: Re: [PATCH v3 11/18] fuse: implement FUSE_INIT map_alignment field Message-ID: <20200826191711.GF3932@work-vm> References: <20200819221956.845195-1-vgoyal@redhat.com> <20200819221956.845195-12-vgoyal@redhat.com> <20200826155142.GA1043442@redhat.com> <20200826173408.GA11480@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200826173408.GA11480@stefanha-x1.localdomain> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Stefan Hajnoczi (stefanha@redhat.com) wrote: > On Wed, Aug 26, 2020 at 11:51:42AM -0400, Vivek Goyal wrote: > > On Wed, Aug 26, 2020 at 04:06:35PM +0200, Miklos Szeredi wrote: > > > On Thu, Aug 20, 2020 at 12:21 AM Vivek Goyal wrote: > > > > > > > > The device communicates FUSE_SETUPMAPPING/FUSE_REMOVMAPPING alignment > > > > constraints via the FUST_INIT map_alignment field. Parse this field and > > > > ensure our DAX mappings meet the alignment constraints. > > > > > > > > We don't actually align anything differently since our mappings are > > > > already 2MB aligned. Just check the value when the connection is > > > > established. If it becomes necessary to honor arbitrary alignments in > > > > the future we'll have to adjust how mappings are sized. > > > > > > > > The upshot of this commit is that we can be confident that mappings will > > > > work even when emulating x86 on Power and similar combinations where the > > > > host page sizes are different. > > > > > > > > Signed-off-by: Stefan Hajnoczi > > > > Signed-off-by: Vivek Goyal > > > > --- > > > > fs/fuse/fuse_i.h | 5 ++++- > > > > fs/fuse/inode.c | 18 ++++++++++++++++-- > > > > include/uapi/linux/fuse.h | 4 +++- > > > > 3 files changed, 23 insertions(+), 4 deletions(-) > > > > > > > > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > > > > index 478c940b05b4..4a46e35222c7 100644 > > > > --- a/fs/fuse/fuse_i.h > > > > +++ b/fs/fuse/fuse_i.h > > > > @@ -47,7 +47,10 @@ > > > > /** Number of dentries for each connection in the control filesystem */ > > > > #define FUSE_CTL_NUM_DENTRIES 5 > > > > > > > > -/* Default memory range size, 2MB */ > > > > +/* > > > > + * Default memory range size. A power of 2 so it agrees with common FUSE_INIT > > > > + * map_alignment values 4KB and 64KB. > > > > + */ > > > > #define FUSE_DAX_SZ (2*1024*1024) > > > > #define FUSE_DAX_SHIFT (21) > > > > #define FUSE_DAX_PAGES (FUSE_DAX_SZ/PAGE_SIZE) > > > > diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c > > > > index b82eb61d63cc..947abdd776ca 100644 > > > > --- a/fs/fuse/inode.c > > > > +++ b/fs/fuse/inode.c > > > > @@ -980,9 +980,10 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_args *args, > > > > { > > > > struct fuse_init_args *ia = container_of(args, typeof(*ia), args); > > > > struct fuse_init_out *arg = &ia->out; > > > > + bool ok = true; > > > > > > > > if (error || arg->major != FUSE_KERNEL_VERSION) > > > > - fc->conn_error = 1; > > > > + ok = false; > > > > else { > > > > unsigned long ra_pages; > > > > > > > > @@ -1045,6 +1046,13 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_args *args, > > > > min_t(unsigned int, FUSE_MAX_MAX_PAGES, > > > > max_t(unsigned int, arg->max_pages, 1)); > > > > } > > > > + if ((arg->flags & FUSE_MAP_ALIGNMENT) && > > > > + (FUSE_DAX_SZ % (1ul << arg->map_alignment))) { > > > > > > This just obfuscates "arg->map_alignment != FUSE_DAX_SHIFT". > > > > > > So the intention was that userspace can ask the kernel for a > > > particular alignment, right? > > > > My understanding is that device will specify alignment for > > the foffset/moffset fields in fuse_setupmapping_in/fuse_removemapping_one. > > And DAX mapping can be any size meeting that alignment contraint. > > > > > > > > In that case kernel can definitely succeed if the requested alignment > > > is smaller than the kernel provided one, no? > > > > Yes. So if map_alignemnt is 64K and DAX mapping size is 2MB, that's just > > fine because it meets 4K alignment contraint. Just that we can't use > > 4K size DAX mapping in that case. > > > > > It would also make > > > sense to make this a two way negotiation. I.e. send the largest > > > alignment (FUSE_DAX_SHIFT in this implementation) that the kernel can > > > provide in fuse_init_in. In that case the only error would be if > > > userspace ignored the given constraints. > > > > We could make it two way negotiation if it helps. So if we support > > multiple mapping sizes in future, say 4K, 64K, 2MB, 1GB. So idea is > > to send alignment of largest mapping size to device/user_space (1GB) > > in this case? And that will allow device to choose an alignment > > which best fits its needs? > > > > But problem here is that sending (log2(1GB)) does not mean we support > > all the alignments in that range. For example, if device selects say > > 256MB as minimum alignment, kernel might not support it. > > > > So there seem to be two ways to handle this. > > > > A.Let device be conservative and always specify the minimum aligment > > it can work with and let guest kernel automatically choose a mapping > > size which meets that min_alignment contraint. > > > > B.Send all the mapping sizes supported by kernel to device and then > > device chooses an alignment as it sees fit. We could probably send > > a 64bit field and set a bit for every size we support as dax mapping. > > If we were to go down this path, I think in that case client should > > respond back with exact mapping size we should use (and not with > > minimum alignment). > > > > I thought intent behind this patch was to implement A. > > > > Stefan/David, this patch came from you folks. What do you think? > > Yes, I agree with Vivek. > > The FUSE server is telling the client the minimum alignment for > foffset/moffset. The client can map any size it likes as long as > foffset/moffset meet the alignment constraint. I can't think of a reason > to do two-way negotiation. Agreed, because there's not much that the server can do about it if the client would like a smaller granularity - the servers granularity might be dictated by it's mmap/pagesize/filesystem. If the client wants a larger granularity that's it's choice when it sends the setupmapping calls. Dave > Stefan -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK