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Date: Thu, 11 Apr 2019 12:23:00 -0400 (EDT) From: Pankaj Gupta <pagupta@...hat.com> To: Dan Williams <dan.j.williams@...el.com> Cc: cohuck@...hat.com, Jan Kara <jack@...e.cz>, KVM list <kvm@...r.kernel.org>, "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, david <david@...morbit.com>, Qemu Developers <qemu-devel@...gnu.org>, virtualization@...ts.linux-foundation.org, Andreas Dilger <adilger.kernel@...ger.ca>, Ross Zwisler <zwisler@...nel.org>, Andrea Arcangeli <aarcange@...hat.com>, Dave Jiang <dave.jiang@...el.com>, linux-nvdimm <linux-nvdimm@...ts.01.org>, Vishal L Verma <vishal.l.verma@...el.com>, David Hildenbrand <david@...hat.com>, Matthew Wilcox <willy@...radead.org>, Christoph Hellwig <hch@...radead.org>, Linux ACPI <linux-acpi@...r.kernel.org>, jmoyer <jmoyer@...hat.com>, linux-ext4 <linux-ext4@...r.kernel.org>, Len Brown <lenb@...nel.org>, kilobyte@...band.pl, Rik van Riel <riel@...riel.com>, yuval shaia <yuval.shaia@...cle.com>, Stefan Hajnoczi <stefanha@...hat.com>, Paolo Bonzini <pbonzini@...hat.com>, lcapitulino@...hat.com, Kevin Wolf <kwolf@...hat.com>, Nitesh Narayan Lal <nilal@...hat.com>, Theodore Ts'o <tytso@....edu>, Xiao Guangrong <xiaoguangrong.eric@...il.com>, "Darrick J. Wong" <darrick.wong@...cle.com>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-xfs <linux-xfs@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Igor Mammedov <imammedo@...hat.com> Subject: Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support > > > > 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> > > > > ---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? > > No, I think you implemented it correctly. I'm just asking for the > chaining to be performed internal to the ->flush() callback rather > than in the common nvdimm_flush() front-end. Sure. Perfect! Thank you very much for all the suggestions. Best regards, Pankaj >
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