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Date: Thu, 11 Apr 2019 07:51:48 -0700 From: Dan Williams <dan.j.williams@...el.com> To: Pankaj Gupta <pagupta@...hat.com> Cc: linux-nvdimm <linux-nvdimm@...ts.01.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, virtualization@...ts.linux-foundation.org, KVM list <kvm@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Linux ACPI <linux-acpi@...r.kernel.org>, Qemu Developers <qemu-devel@...gnu.org>, linux-ext4 <linux-ext4@...r.kernel.org>, linux-xfs <linux-xfs@...r.kernel.org>, Ross Zwisler <zwisler@...nel.org>, Vishal L Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, Matthew Wilcox <willy@...radead.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Christoph Hellwig <hch@...radead.org>, Len Brown <lenb@...nel.org>, Jan Kara <jack@...e.cz>, "Theodore Ts'o" <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>, "Darrick J. Wong" <darrick.wong@...cle.com>, lcapitulino@...hat.com, Kevin Wolf <kwolf@...hat.com>, Igor Mammedov <imammedo@...hat.com>, jmoyer <jmoyer@...hat.com>, Nitesh Narayan Lal <nilal@...hat.com>, Rik van Riel <riel@...riel.com>, Stefan Hajnoczi <stefanha@...hat.com>, Andrea Arcangeli <aarcange@...hat.com>, David Hildenbrand <david@...hat.com>, david <david@...morbit.com>, cohuck@...hat.com, Xiao Guangrong <xiaoguangrong.eric@...il.com>, Paolo Bonzini <pbonzini@...hat.com>, kilobyte@...band.pl, yuval.shaia@...cle.com Subject: Re: [PATCH v5 1/6] libnvdimm: nd_region flush callback support On Tue, Apr 9, 2019 at 9:09 PM Pankaj Gupta <pagupta@...hat.com> wrote: > > 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@...hat.com> > --- [..] > 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) ...so why not gate async behavior on the presence of the 'bio' argument? > + 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. > + } 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(...);
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