From: Dan Williams <dan.j.williams@intel.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Pankaj Gupta <pagupta@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
KVM list <kvm@vger.kernel.org>,
Qemu Developers <qemu-devel@nongnu.org>,
linux-nvdimm <linux-nvdimm@ml01.01.org>,
Linux MM <linux-mm@kvack.org>, Jan Kara <jack@suse.cz>,
Stefan Hajnoczi <stefanha@redhat.com>,
Rik van Riel <riel@redhat.com>,
haozhong zhang <haozhong.zhang@intel.com>,
Nitesh Narayan Lal <nilal@redhat.com>,
Kevin Wolf <kwolf@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
ross zwisler <ross.zwisler@intel.com>,
David Hildenbrand <david@redhat.com>,
xiaoguangrong eric <xiaoguangrong.eric@gmail.com>
Subject: Re: [RFC 2/2] KVM: add virtio-pmem driver
Date: Mon, 16 Oct 2017 08:58:37 -0700 [thread overview]
Message-ID: <CAPcyv4hffSdoONfFohKZzfB2gywGYG9MmDxC0H9+5R53w+ROVQ@mail.gmail.com> (raw)
In-Reply-To: <20171016144753.GB14135@stefanha-x1.localdomain>
On Mon, Oct 16, 2017 at 7:47 AM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
> On Fri, Oct 13, 2017 at 06:48:15AM -0400, Pankaj Gupta wrote:
>> > On Thu, Oct 12, 2017 at 09:20:26PM +0530, Pankaj Gupta wrote:
>> > > +static blk_qc_t virtio_pmem_make_request(struct request_queue *q,
>> > > + struct bio *bio)
>> > > +{
>> > > + blk_status_t rc = 0;
>> > > + struct bio_vec bvec;
>> > > + struct bvec_iter iter;
>> > > + struct virtio_pmem *pmem = q->queuedata;
>> > > +
>> > > + if (bio->bi_opf & REQ_FLUSH)
>> > > + //todo host flush command
>> >
>> > This detail is critical to the device design. What is the plan?
>>
>> yes, this is good point.
>>
>> was thinking of guest sending a flush command to Qemu which
>> will do a fsync on file fd.
>
> Previously there was discussion about fsyncing a specific file range
> instead of the whole file. This could perform better in cases where
> only a subset of dirty pages need to be flushed.
>
> One possibility is to design the virtio interface to communicate ranges
> but the emulation code simply fsyncs the fd for the time being. Later
> on, if the necessary kernel and userspace interfaces are added, we can
> make use of the interface.
Range based is not a natural storage cache management mechanism. All
that is it available typically is a full write-cache-flush mechanism
and upper layers would need to customized for range-based flushing.
>> If we do a async flush and move the task to wait queue till we receive
>> flush complete reply from host we can allow other tasks to execute
>> in current cpu.
>>
>> Any suggestions you have or anything I am not foreseeing here?
>
> My main thought about this patch series is whether pmem should be a
> virtio-blk feature bit instead of a whole new device. There is quite a
> bit of overlap between the two.
I'd be open to that... there's already provisions in the pmem driver
for platforms where cpu caches are flushed on power-loss, a virtio
mode for this shared-memory case seems reasonable.
next prev parent reply other threads:[~2017-10-16 15:58 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-12 15:50 [RFC 0/2] KVM "fake DAX" device flushing Pankaj Gupta
2017-10-12 15:50 ` [RFC 1/2] pmem: Move reusable code to base header files Pankaj Gupta
2017-10-12 20:42 ` Dan Williams
2017-10-12 21:27 ` [Qemu-devel] " Pankaj Gupta
[not found] ` <20171012155027.3277-1-pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-10-12 15:50 ` [RFC 2/2] KVM: add virtio-pmem driver Pankaj Gupta
2017-10-12 20:51 ` Dan Williams
2017-10-12 21:25 ` Pankaj Gupta
2017-10-12 21:54 ` Dan Williams
[not found] ` <CAPcyv4gkri7t+3Unf0sc9AHMnz-v9G_qV_bJppLjUUNAn7drrQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-10-12 22:18 ` Pankaj Gupta
2017-10-12 22:27 ` Rik van Riel
2017-10-12 22:39 ` Pankaj Gupta
2017-10-12 22:52 ` Pankaj Gupta
2017-10-12 22:59 ` Dan Williams
2017-10-12 23:07 ` Pankaj Gupta
2017-10-13 9:44 ` Stefan Hajnoczi
2017-10-13 10:48 ` Pankaj Gupta
[not found] ` <24301306.20068579.1507891695416.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-10-16 14:47 ` Stefan Hajnoczi
2017-10-16 15:58 ` Dan Williams [this message]
2017-10-16 17:04 ` Pankaj Gupta
[not found] ` <20171013094431.GA27308-lxVrvc10SDRcolVlb+j0YCZi+YwRKgec@public.gmane.org>
2017-10-13 15:25 ` Dan Williams
[not found] ` <20171012155027.3277-3-pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-10-17 7:16 ` Christoph Hellwig
2017-10-17 7:40 ` [Qemu-devel] " Pankaj Gupta
2017-10-17 8:02 ` Christoph Hellwig
2017-10-17 8:30 ` Pankaj Gupta
2017-10-18 13:03 ` Stefan Hajnoczi
2017-10-18 15:51 ` Dan Williams
[not found] ` <CAPcyv4h6aFkyHhh4R4DTznbSCLf9CuBoszk0Q1gB5EKNcp_SeQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-10-19 8:01 ` Stefan Hajnoczi
2017-10-19 8:01 ` Christoph Hellwig
[not found] ` <20171019080149.GB10089-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-10-19 18:21 ` Dan Williams
[not found] ` <CAPcyv4j=Cdp68C15HddKaErpve2UGRfSTiL6bHiS=3gQybz9pg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-10-20 8:00 ` Christoph Hellwig
[not found] ` <20171020080049.GA25471-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-10-20 15:05 ` Dan Williams
2017-10-20 16:06 ` Christoph Hellwig
2017-10-20 16:11 ` Dan Williams
2017-10-12 15:50 ` [RFC] QEMU: Add virtio pmem device Pankaj Gupta
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