From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stefan Hajnoczi <stefanha@gmail.com>
Subject: Re: [Qemu-devel] [RFC 2/2] KVM: add virtio-pmem driver
Date: Wed, 18 Oct 2017 15:03:39 +0200
Message-ID: <20171018130339.GB29767@stefanha-x1.localdomain>
References: <20171012155027.3277-1-pagupta@redhat.com>
 <20171012155027.3277-3-pagupta@redhat.com>
 <20171017071633.GA9207@infradead.org>
 <1441791227.21027037.1508226056893.JavaMail.zimbra@redhat.com>
 <20171017080236.GA27649@infradead.org>
 <670833322.21037148.1508229041158.JavaMail.zimbra@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <owner-linux-mm@kvack.org>
Content-Disposition: inline
In-Reply-To: <670833322.21037148.1508229041158.JavaMail.zimbra@redhat.com>
Sender: owner-linux-mm@kvack.org
To: Pankaj Gupta <pagupta@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>, kwolf@redhat.com, haozhong zhang <haozhong.zhang@intel.com>, jack@suse.cz, xiaoguangrong eric <xiaoguangrong.eric@gmail.com>, kvm@vger.kernel.org, david@redhat.com, linux-nvdimm@ml01.01.org, ross zwisler <ross.zwisler@intel.com>, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, linux-mm@kvack.org, stefanha@redhat.com, pbonzini@redhat.com, dan j williams <dan.j.williams@intel.com>, nilal@redhat.com
List-Id: linux-nvdimm@lists.01.org

On Tue, Oct 17, 2017 at 04:30:41AM -0400, Pankaj Gupta wrote:
> 
> > > Are you saying do it as existing i.e ACPI pmem like interface?
> > > The reason we have created this new driver is exiting pmem driver
> > > does not define proper semantics for guest flushing requests.
> > 
> > At this point I'm caring about the Linux-internal interface, and
> > for that it should be integrated into the nvdimm subsystem and not
> > a block driver.  How the host <-> guest interface looks is a different
> > idea.
> > 
> > > 
> > > Regarding block support of driver, we want to achieve DAX support
> > > to bypass guest page cache. Also, we want to utilize existing DAX
> > > capable file-system interfaces(e.g fsync) from userspace file API's
> > > to trigger the host side flush request.
> > 
> > Well, if you want to support XFS+DAX better don't make it a block
> > devices, because I'll post patches soon to stop using the block device
> > entirely for the DAX case.
> 
> o.k I will look at your patches once they are in mailing list.
> Thanks for the heads up.
> 
> If I am guessing it right, we don't need block device additional features
> for pmem? We can bypass block device features like blk device cache flush etc.
> Also, still we would be supporting ext4 & XFS filesystem with pmem?
> 
> If there is time to your patches can you please elaborate on this a bit.

I think the idea is that the nvdimm subsystem already adds block device
semantics on top of the struct nvdimms that it manages.  See
drivers/nvdimm/blk.c.

So it would be cleaner to make virtio-pmem an nvdimm bus.  This will
eliminate the duplication between your driver and drivers/nvdimm/ code.
Try "git grep nvdimm_bus_register" to find drivers that use the nvdimm
subsystem.

The virtio-pmem driver could register itself similar to the existing
ACPI NFIT and BIOS e820 pmem drivers.

Stefan

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1753101AbdJRNDr (ORCPT <rfc822;w@1wt.eu>);
        Wed, 18 Oct 2017 09:03:47 -0400
Received: from mail-wm0-f67.google.com ([74.125.82.67]:55330 "EHLO
        mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1753066AbdJRNDn (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 18 Oct 2017 09:03:43 -0400
X-Google-Smtp-Source: ABhQp+R4utEHeBYcfDgg8rREjB644400ru+KjOmOfYgi3OI8MwPQ090DF7ncpFw3K1x8V8S0NsLUmQ==
Date: Wed, 18 Oct 2017 15:03:39 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
To: Pankaj Gupta <pagupta@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>, kwolf@redhat.com,
        haozhong zhang <haozhong.zhang@intel.com>, jack@suse.cz,
        xiaoguangrong eric <xiaoguangrong.eric@gmail.com>, kvm@vger.kernel.org,
        david@redhat.com, linux-nvdimm@ml01.01.org,
        ross zwisler <ross.zwisler@intel.com>, linux-kernel@vger.kernel.org,
        qemu-devel@nongnu.org, linux-mm@kvack.org, stefanha@redhat.com,
        pbonzini@redhat.com, dan j williams <dan.j.williams@intel.com>,
        nilal@redhat.com
Subject: Re: [Qemu-devel] [RFC 2/2] KVM: add virtio-pmem driver
Message-ID: <20171018130339.GB29767@stefanha-x1.localdomain>
References: <20171012155027.3277-1-pagupta@redhat.com>
 <20171012155027.3277-3-pagupta@redhat.com>
 <20171017071633.GA9207@infradead.org>
 <1441791227.21027037.1508226056893.JavaMail.zimbra@redhat.com>
 <20171017080236.GA27649@infradead.org>
 <670833322.21037148.1508229041158.JavaMail.zimbra@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <670833322.21037148.1508229041158.JavaMail.zimbra@redhat.com>
User-Agent: Mutt/1.9.1 (2017-09-22)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Oct 17, 2017 at 04:30:41AM -0400, Pankaj Gupta wrote:
> 
> > > Are you saying do it as existing i.e ACPI pmem like interface?
> > > The reason we have created this new driver is exiting pmem driver
> > > does not define proper semantics for guest flushing requests.
> > 
> > At this point I'm caring about the Linux-internal interface, and
> > for that it should be integrated into the nvdimm subsystem and not
> > a block driver.  How the host <-> guest interface looks is a different
> > idea.
> > 
> > > 
> > > Regarding block support of driver, we want to achieve DAX support
> > > to bypass guest page cache. Also, we want to utilize existing DAX
> > > capable file-system interfaces(e.g fsync) from userspace file API's
> > > to trigger the host side flush request.
> > 
> > Well, if you want to support XFS+DAX better don't make it a block
> > devices, because I'll post patches soon to stop using the block device
> > entirely for the DAX case.
> 
> o.k I will look at your patches once they are in mailing list.
> Thanks for the heads up.
> 
> If I am guessing it right, we don't need block device additional features
> for pmem? We can bypass block device features like blk device cache flush etc.
> Also, still we would be supporting ext4 & XFS filesystem with pmem?
> 
> If there is time to your patches can you please elaborate on this a bit.

I think the idea is that the nvdimm subsystem already adds block device
semantics on top of the struct nvdimms that it manages.  See
drivers/nvdimm/blk.c.

So it would be cleaner to make virtio-pmem an nvdimm bus.  This will
eliminate the duplication between your driver and drivers/nvdimm/ code.
Try "git grep nvdimm_bus_register" to find drivers that use the nvdimm
subsystem.

The virtio-pmem driver could register itself similar to the existing
ACPI NFIT and BIOS e820 pmem drivers.

Stefan