From: Pankaj Gupta <pagupta@redhat.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: cohuck@redhat.com, Jan Kara <jack@suse.cz>,
KVM list <kvm@vger.kernel.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
Jason Wang <jasowang@redhat.com>, david <david@fromorbit.com>,
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virtualization@lists.linux-foundation.org,
Andreas Dilger <adilger.kernel@dilger.ca>,
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Vishal L Verma <vishal.l.verma@intel.com>,
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Igor Mammedov <imammedo@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support
Date: Thu, 11 Apr 2019 11:57:38 -0400 (EDT) [thread overview]
Message-ID: <1463291806.21158433.1554998258746.JavaMail.zimbra@redhat.com> (raw)
In-Reply-To: <CAPcyv4i1FjBzfcWtzeCvj-giHa9xaX0dMQ==q4LZC_L8VEqkHg@mail.gmail.com>
> >
> > This patch adds functionality to perform flush from guest
> > to host over VIRTIO. We are registering a callback based
> > on 'nd_region' type. virtio_pmem driver requires this special
> > flush function. For rest of the region types we are registering
> > existing flush function. Report error returned by host fsync
> > failure to userspace.
> >
> > This also handles asynchronous flush requests from the block layer
> > by creating a child bio and chaining it with parent bio.
> >
> > Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> > ---bio_chain Dan williams
> [..]
> > diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
> > index b4ef7d9ff22e..fb1041ab32a6 100644
> > --- a/drivers/nvdimm/region_devs.c
> > +++ b/drivers/nvdimm/region_devs.c
> > @@ -295,7 +295,9 @@ static ssize_t deep_flush_store(struct device *dev,
> > struct device_attribute *att
> > return rc;
> > if (!flush)
> > return -EINVAL;
> > - nvdimm_flush(nd_region);
> > + rc = nvdimm_flush(nd_region, NULL, false);
> > + if (rc)
> > + return rc;
> >
> > return len;
> > }
> > @@ -1085,6 +1087,11 @@ static struct nd_region *nd_region_create(struct
> > nvdimm_bus *nvdimm_bus,
> > dev->of_node = ndr_desc->of_node;
> > nd_region->ndr_size = resource_size(ndr_desc->res);
> > nd_region->ndr_start = ndr_desc->res->start;
> > + if (ndr_desc->flush)
> > + nd_region->flush = ndr_desc->flush;
> > + else
> > + nd_region->flush = generic_nvdimm_flush;
> > +
> > nd_device_register(dev);
> >
> > return nd_region;
> > @@ -1125,11 +1132,36 @@ struct nd_region
> > *nvdimm_volatile_region_create(struct nvdimm_bus *nvdimm_bus,
> > }
> > EXPORT_SYMBOL_GPL(nvdimm_volatile_region_create);
> >
> > +int nvdimm_flush(struct nd_region *nd_region, struct bio *bio, bool async)
> > +{
>
> I don't quite see the point of the 'async' argument. All the usages of
> this routine are either
>
> nvdimm_flush(nd_region, bio, true)
> ...or:
> nvdimm_flush(nd_region, NULL, false)
Agree.
>
> ...so why not gate async behavior on the presence of the 'bio' argument?
Sure.
>
>
> > + int rc = 0;
> > +
> > + /* Create child bio for asynchronous flush and chain with
> > + * parent bio. Otherwise directly call nd_region flush.
> > + */
> > + if (async && bio->bi_iter.bi_sector != -1) {
> > +
> > + struct bio *child = bio_alloc(GFP_ATOMIC, 0);
> > +
> > + if (!child)
> > + return -ENOMEM;
> > + bio_copy_dev(child, bio);
> > + child->bi_opf = REQ_PREFLUSH;
> > + child->bi_iter.bi_sector = -1;
> > + bio_chain(child, bio);
> > + submit_bio(child);
>
> I understand how this works, but it's a bit too "magical" for my
> taste. I would prefer that all flush implementations take an optional
> 'bio' argument rather than rely on the make_request implementation to
> stash the bio away on a driver specific list.
I did this to make use of "bio_chain" for chaining child bio for async flush
suggested [1]. Are you saying to remove this and just call "flush" based on
bio argument? Or I implemented the 'bio_chain' request entirely wrong?
[1] https://lkml.org/lkml/2018/9/27/1028
>
> > + } else {
> > + if (nd_region->flush(nd_region))
> > + rc = -EIO;
>
> Given the common case wants to be fast and synchronous I think we
> should try to avoid retpoline overhead by default. So something like
> this:
>
> if (nd_region->flush == generic_nvdimm_flush)
> rc = generic_nvdimm_flush(...);
Sure.
Thanks,
Pankaj
>
>
next prev parent reply other threads:[~2019-04-11 15:57 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-10 4:08 [PATCH v5 0/6] virtio pmem driver Pankaj Gupta
2019-04-10 4:08 ` [PATCH v5 1/6] libnvdimm: nd_region flush callback support Pankaj Gupta
2019-04-11 14:51 ` Dan Williams
2019-04-11 15:57 ` Pankaj Gupta [this message]
2019-04-11 16:09 ` [Qemu-devel] " Dan Williams
2019-04-11 16:23 ` Pankaj Gupta
2019-04-12 8:32 ` Jan Kara
2019-04-12 13:12 ` Jeff Moyer
2019-04-18 6:27 ` [Qemu-devel] " Pankaj Gupta
2019-04-18 16:05 ` Dan Williams
2019-04-18 16:10 ` Jeff Moyer
2019-04-18 16:18 ` Christoph Hellwig
2019-04-18 18:14 ` Dan Williams
2019-04-22 15:51 ` Jeff Moyer
2019-04-22 19:44 ` Dan Williams
2019-04-22 21:03 ` Jeff Moyer
2019-04-23 4:07 ` Pankaj Gupta
2019-04-10 4:08 ` [PATCH v5 2/5] virtio-pmem: Add virtio pmem driver Pankaj Gupta
2019-04-10 12:24 ` Cornelia Huck
2019-04-10 14:38 ` Yuval Shaia
2019-04-10 15:44 ` Pankaj Gupta
2019-04-10 15:38 ` Pankaj Gupta
2019-04-10 13:12 ` Michael S. Tsirkin
2019-04-10 14:03 ` [Qemu-devel] " Pankaj Gupta
2019-04-10 14:31 ` Cornelia Huck
2019-04-10 16:46 ` Michael S. Tsirkin
2019-04-10 16:52 ` Cornelia Huck
2019-04-10 14:41 ` Yuval Shaia
2019-04-10 4:08 ` [PATCH v5 3/6] libnvdimm: add dax_dev sync flag Pankaj Gupta
2019-04-10 8:28 ` Jan Kara
2019-04-10 8:38 ` Pankaj Gupta
2019-04-11 14:56 ` Dan Williams
2019-04-11 15:39 ` Pankaj Gupta
2019-04-10 4:08 ` [PATCH v5 4/6] dax: check synchronous mapping is supported Pankaj Gupta
2019-04-10 8:25 ` Jan Kara
2019-04-10 8:31 ` Pankaj Gupta
2019-04-10 4:08 ` [PATCH v5 5/6] ext4: disable map_sync for async flush Pankaj Gupta
2019-04-10 4:08 ` [PATCH v5 6/6] xfs: " Pankaj Gupta
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