Re: [RFC v2 1/2] virtio-pmem: Async virtio-pmem flush
> > > > > > Implement asynchronous flush for virtio pmem using work queue
> > > > > > to solve the preflush ordering issue. Also, coalesce the flush
> > > > > > requests when a flush is already in process.
> > > > > >
> > > > > > Signed-off-by: Pankaj Gupta
> > > > > > ---
> > > > > > drivers/nvdimm/nd_virtio.c | 72
> > > > > >
> > > > > > drivers/nvdimm/virtio_pmem.c | 10 -
> > > > > > drivers/nvdimm/virtio_pmem.h | 14 +++
> > > > > > 3 files changed, 79 insertions(+), 17 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
> > > > > > index 10351d5b49fa..61b655b583be 100644
> > > > > > --- a/drivers/nvdimm/nd_virtio.c
> > > > > > +++ b/drivers/nvdimm/nd_virtio.c
> > > > > > @@ -97,29 +97,69 @@ static int virtio_pmem_flush(struct nd_region
> > > > > > *nd_region)
> > > > > > return err;
> > > > > > };
> > > > > >
> > > > > > +static void submit_async_flush(struct work_struct *ws);
> > > > > > +
> > > > > > /* The asynchronous flush callback function */
> > > > > > int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
> > > > > > {
> > > > > > - /*
> > > > > > -* Create child bio for asynchronous flush and chain with
> > > > > > -* parent bio. Otherwise directly call nd_region flush.
> > > > > > + /* queue asynchronous flush and coalesce the flush requests
> > > > > > */
> > > > > > + struct virtio_device *vdev = nd_region->provider_data;
> > > > > > + struct virtio_pmem *vpmem = vdev->priv;
> > > > > > + ktime_t req_start = ktime_get_boottime();
> > > > > > +
> > > > > > + spin_lock_irq(&vpmem->lock);
> > > > > > + /* flush requests wait until ongoing flush completes,
> > > > > > +* hence coalescing all the pending requests.
> > > > > > */
> > > > > > - if (bio && 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);
> > > > > > - return 0;
> > > > > > + wait_event_lock_irq(vpmem->sb_wait,
> > > > > > + !vpmem->flush_bio ||
> > > > > > + ktime_before(req_start,
> > > > > > vpmem->prev_flush_start),
> > > > > > + vpmem->lock);
> > > > > > + /* new request after previous flush is completed */
> > > > > > + if (ktime_after(req_start, vpmem->prev_flush_start)) {
> > > > > > + WARN_ON(vpmem->flush_bio);
> > > > > > + vpmem->flush_bio = bio;
> > > > > > + bio = NULL;
> > > > > > + }
> > > > >
> > > > > Why the dance with ->prev_flush_start vs just calling queue_work()
> > > > > again. queue_work() is naturally coalescing in that if the last work
> > > > > request has not started execution another queue attempt will be
> > > > > dropped.
> > > >
> > > > How parent flush request will know when corresponding flush is
> > > > completed?
> > >
> > > The eventual bio_endio() is what signals upper layers that the flush
> > > completed...
> > >
> > >
> > > Hold on... it's been so long that I forgot that you are copying
> > > md_flush_request() here. It would help immensely if that was mentioned
> > > in the changelog and at a minimum have a comment in the code that this
> > > was copied from md. In fact it would be extra helpful if you
> >
> > My bad. I only mentioned this in the cover letter.
>
> Yeah, sorry about that. Having come back to this after so long I just
> decided to jump straight into the patches, but even if I had read that
> cover I still would have given the feedback that md_flush_request()
> heritage should also be noted with a comment in the code.
Sure.
Thanks,
Pankaj
Re: [RFC v2 1/2] virtio-pmem: Async virtio-pmem flush
On Wed, Aug 25, 2021 at 3:01 PM Pankaj Gupta wrote:
>
> > > Hi Dan,
> > >
> > > Thank you for the review. Please see my reply inline.
> > >
> > > > > Implement asynchronous flush for virtio pmem using work queue
> > > > > to solve the preflush ordering issue. Also, coalesce the flush
> > > > > requests when a flush is already in process.
> > > > >
> > > > > Signed-off-by: Pankaj Gupta
> > > > > ---
> > > > > drivers/nvdimm/nd_virtio.c | 72
> > > > >
> > > > > drivers/nvdimm/virtio_pmem.c | 10 -
> > > > > drivers/nvdimm/virtio_pmem.h | 14 +++
> > > > > 3 files changed, 79 insertions(+), 17 deletions(-)
> > > > >
> > > > > diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
> > > > > index 10351d5b49fa..61b655b583be 100644
> > > > > --- a/drivers/nvdimm/nd_virtio.c
> > > > > +++ b/drivers/nvdimm/nd_virtio.c
> > > > > @@ -97,29 +97,69 @@ static int virtio_pmem_flush(struct nd_region
> > > > > *nd_region)
> > > > > return err;
> > > > > };
> > > > >
> > > > > +static void submit_async_flush(struct work_struct *ws);
> > > > > +
> > > > > /* The asynchronous flush callback function */
> > > > > int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
> > > > > {
> > > > > - /*
> > > > > -* Create child bio for asynchronous flush and chain with
> > > > > -* parent bio. Otherwise directly call nd_region flush.
> > > > > + /* queue asynchronous flush and coalesce the flush requests */
> > > > > + struct virtio_device *vdev = nd_region->provider_data;
> > > > > + struct virtio_pmem *vpmem = vdev->priv;
> > > > > + ktime_t req_start = ktime_get_boottime();
> > > > > +
> > > > > + spin_lock_irq(&vpmem->lock);
> > > > > + /* flush requests wait until ongoing flush completes,
> > > > > +* hence coalescing all the pending requests.
> > > > > */
> > > > > - if (bio && 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);
> > > > > - return 0;
> > > > > + wait_event_lock_irq(vpmem->sb_wait,
> > > > > + !vpmem->flush_bio ||
> > > > > + ktime_before(req_start,
> > > > > vpmem->prev_flush_start),
> > > > > + vpmem->lock);
> > > > > + /* new request after previous flush is completed */
> > > > > + if (ktime_after(req_start, vpmem->prev_flush_start)) {
> > > > > + WARN_ON(vpmem->flush_bio);
> > > > > + vpmem->flush_bio = bio;
> > > > > + bio = NULL;
> > > > > + }
> > > >
> > > > Why the dance with ->prev_flush_start vs just calling queue_work()
> > > > again. queue_work() is naturally coalescing in that if the last work
> > > > request has not started execution another queue attempt will be
> > > > dropped.
> > >
> > > How parent flush request will know when corresponding flush is completed?
> >
> > The eventual bio_endio() is what signals upper layers that the flush
> > completed...
> >
> >
> > Hold on... it's been so long that I forgot that you are copying
> > md_flush_request() here. It would help immensely if that was mentioned
> > in the changelog and at a minimum have a comment in the code that this
> > was copied from md. In fact it would be extra helpful if you
>
> My bad. I only mentioned this in the cover letter.
Yeah, sorry about that. Having come back to this after so long I just
decided to jump straight into the patches, but even if I had read that
cover I still would have given the feedback that md_flush_request()
heritage should also be noted with a comment in the code.
Re: [RFC v2 1/2] virtio-pmem: Async virtio-pmem flush
> > Hi Dan,
> >
> > Thank you for the review. Please see my reply inline.
> >
> > > > Implement asynchronous flush for virtio pmem using work queue
> > > > to solve the preflush ordering issue. Also, coalesce the flush
> > > > requests when a flush is already in process.
> > > >
> > > > Signed-off-by: Pankaj Gupta
> > > > ---
> > > > drivers/nvdimm/nd_virtio.c | 72
> > > > drivers/nvdimm/virtio_pmem.c | 10 -
> > > > drivers/nvdimm/virtio_pmem.h | 14 +++
> > > > 3 files changed, 79 insertions(+), 17 deletions(-)
> > > >
> > > > diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
> > > > index 10351d5b49fa..61b655b583be 100644
> > > > --- a/drivers/nvdimm/nd_virtio.c
> > > > +++ b/drivers/nvdimm/nd_virtio.c
> > > > @@ -97,29 +97,69 @@ static int virtio_pmem_flush(struct nd_region
> > > > *nd_region)
> > > > return err;
> > > > };
> > > >
> > > > +static void submit_async_flush(struct work_struct *ws);
> > > > +
> > > > /* The asynchronous flush callback function */
> > > > int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
> > > > {
> > > > - /*
> > > > -* Create child bio for asynchronous flush and chain with
> > > > -* parent bio. Otherwise directly call nd_region flush.
> > > > + /* queue asynchronous flush and coalesce the flush requests */
> > > > + struct virtio_device *vdev = nd_region->provider_data;
> > > > + struct virtio_pmem *vpmem = vdev->priv;
> > > > + ktime_t req_start = ktime_get_boottime();
> > > > +
> > > > + spin_lock_irq(&vpmem->lock);
> > > > + /* flush requests wait until ongoing flush completes,
> > > > +* hence coalescing all the pending requests.
> > > > */
> > > > - if (bio && 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);
> > > > - return 0;
> > > > + wait_event_lock_irq(vpmem->sb_wait,
> > > > + !vpmem->flush_bio ||
> > > > + ktime_before(req_start,
> > > > vpmem->prev_flush_start),
> > > > + vpmem->lock);
> > > > + /* new request after previous flush is completed */
> > > > + if (ktime_after(req_start, vpmem->prev_flush_start)) {
> > > > + WARN_ON(vpmem->flush_bio);
> > > > + vpmem->flush_bio = bio;
> > > > + bio = NULL;
> > > > + }
> > >
> > > Why the dance with ->prev_flush_start vs just calling queue_work()
> > > again. queue_work() is naturally coalescing in that if the last work
> > > request has not started execution another queue attempt will be
> > > dropped.
> >
> > How parent flush request will know when corresponding flush is completed?
>
> The eventual bio_endio() is what signals upper layers that the flush
> completed...
>
>
> Hold on... it's been so long that I forgot that you are copying
> md_flush_request() here. It would help immensely if that was mentioned
> in the changelog and at a minimum have a comment in the code that this
> was copied from md. In fact it would be extra helpful if you
My bad. I only mentioned this in the cover letter.
> refactored a common helper that bio based block drivers could share
> for implementing flush handling, but that can come later.
Sure.
>
> Let me go re-review this with respect to whether the md case is fully
> applicable here.
o.k.
Best regards,
Pankaj
Re: [RFC v2 1/2] virtio-pmem: Async virtio-pmem flush
On Wed, Aug 25, 2021 at 1:02 PM Pankaj Gupta
wrote:
>
> Hi Dan,
>
> Thank you for the review. Please see my reply inline.
>
> > > Implement asynchronous flush for virtio pmem using work queue
> > > to solve the preflush ordering issue. Also, coalesce the flush
> > > requests when a flush is already in process.
> > >
> > > Signed-off-by: Pankaj Gupta
> > > ---
> > > drivers/nvdimm/nd_virtio.c | 72
> > > drivers/nvdimm/virtio_pmem.c | 10 -
> > > drivers/nvdimm/virtio_pmem.h | 14 +++
> > > 3 files changed, 79 insertions(+), 17 deletions(-)
> > >
> > > diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
> > > index 10351d5b49fa..61b655b583be 100644
> > > --- a/drivers/nvdimm/nd_virtio.c
> > > +++ b/drivers/nvdimm/nd_virtio.c
> > > @@ -97,29 +97,69 @@ static int virtio_pmem_flush(struct nd_region
> > > *nd_region)
> > > return err;
> > > };
> > >
> > > +static void submit_async_flush(struct work_struct *ws);
> > > +
> > > /* The asynchronous flush callback function */
> > > int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
> > > {
> > > - /*
> > > -* Create child bio for asynchronous flush and chain with
> > > -* parent bio. Otherwise directly call nd_region flush.
> > > + /* queue asynchronous flush and coalesce the flush requests */
> > > + struct virtio_device *vdev = nd_region->provider_data;
> > > + struct virtio_pmem *vpmem = vdev->priv;
> > > + ktime_t req_start = ktime_get_boottime();
> > > +
> > > + spin_lock_irq(&vpmem->lock);
> > > + /* flush requests wait until ongoing flush completes,
> > > +* hence coalescing all the pending requests.
> > > */
> > > - if (bio && 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);
> > > - return 0;
> > > + wait_event_lock_irq(vpmem->sb_wait,
> > > + !vpmem->flush_bio ||
> > > + ktime_before(req_start,
> > > vpmem->prev_flush_start),
> > > + vpmem->lock);
> > > + /* new request after previous flush is completed */
> > > + if (ktime_after(req_start, vpmem->prev_flush_start)) {
> > > + WARN_ON(vpmem->flush_bio);
> > > + vpmem->flush_bio = bio;
> > > + bio = NULL;
> > > + }
> >
> > Why the dance with ->prev_flush_start vs just calling queue_work()
> > again. queue_work() is naturally coalescing in that if the last work
> > request has not started execution another queue attempt will be
> > dropped.
>
> How parent flush request will know when corresponding flush is completed?
The eventual bio_endio() is what signals upper layers that the flush
completed...
Hold on... it's been so long that I forgot that you are copying
md_flush_request() here. It would help immensely if that was mentioned
in the changelog and at a minimum have a comment in the code that this
was copied from md. In fact it would be extra helpful if you
refactored a common helper that bio based block drivers could share
for implementing flush handling, but that can come later.
Let me go re-review this with respect to whether the md case is fully
applicable here.
Re: [RFC v2 1/2] virtio-pmem: Async virtio-pmem flush
Hi Dan,
Thank you for the review. Please see my reply inline.
> > Implement asynchronous flush for virtio pmem using work queue
> > to solve the preflush ordering issue. Also, coalesce the flush
> > requests when a flush is already in process.
> >
> > Signed-off-by: Pankaj Gupta
> > ---
> > drivers/nvdimm/nd_virtio.c | 72
> > drivers/nvdimm/virtio_pmem.c | 10 -
> > drivers/nvdimm/virtio_pmem.h | 14 +++
> > 3 files changed, 79 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
> > index 10351d5b49fa..61b655b583be 100644
> > --- a/drivers/nvdimm/nd_virtio.c
> > +++ b/drivers/nvdimm/nd_virtio.c
> > @@ -97,29 +97,69 @@ static int virtio_pmem_flush(struct nd_region
> > *nd_region)
> > return err;
> > };
> >
> > +static void submit_async_flush(struct work_struct *ws);
> > +
> > /* The asynchronous flush callback function */
> > int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
> > {
> > - /*
> > -* Create child bio for asynchronous flush and chain with
> > -* parent bio. Otherwise directly call nd_region flush.
> > + /* queue asynchronous flush and coalesce the flush requests */
> > + struct virtio_device *vdev = nd_region->provider_data;
> > + struct virtio_pmem *vpmem = vdev->priv;
> > + ktime_t req_start = ktime_get_boottime();
> > +
> > + spin_lock_irq(&vpmem->lock);
> > + /* flush requests wait until ongoing flush completes,
> > +* hence coalescing all the pending requests.
> > */
> > - if (bio && 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);
> > - return 0;
> > + wait_event_lock_irq(vpmem->sb_wait,
> > + !vpmem->flush_bio ||
> > + ktime_before(req_start,
> > vpmem->prev_flush_start),
> > + vpmem->lock);
> > + /* new request after previous flush is completed */
> > + if (ktime_after(req_start, vpmem->prev_flush_start)) {
> > + WARN_ON(vpmem->flush_bio);
> > + vpmem->flush_bio = bio;
> > + bio = NULL;
> > + }
>
> Why the dance with ->prev_flush_start vs just calling queue_work()
> again. queue_work() is naturally coalescing in that if the last work
> request has not started execution another queue attempt will be
> dropped.
How parent flush request will know when corresponding flush is completed?
>
> > + spin_unlock_irq(&vpmem->lock);
> > +
> > + if (!bio) {
> > + INIT_WORK(&vpmem->flush_work, submit_async_flush);
>
> I expect this only needs to be initialized once at driver init time.
yes, will fix this.
>
> > + queue_work(vpmem->pmem_wq, &vpmem->flush_work);
> > + return 1;
> > + }
> > +
> > + /* flush completed in other context while we waited */
> > + if (bio && (bio->bi_opf & REQ_PREFLUSH)) {
> > + bio->bi_opf &= ~REQ_PREFLUSH;
> > + submit_bio(bio);
> > + } else if (bio && (bio->bi_opf & REQ_FUA)) {
> > + bio->bi_opf &= ~REQ_FUA;
> > + bio_endio(bio);
>
> It's not clear to me how this happens, shouldn't all flush completions
> be driven from the work completion?
Requests should progress after notified by ongoing flush completion
event.
>
> > }
> > - if (virtio_pmem_flush(nd_region))
> > - return -EIO;
> >
> > return 0;
> > };
> > EXPORT_SYMBOL_GPL(async_pmem_flush);
> > +
> > +static void submit_async_flush(struct work_struct *ws)
> > +{
> > + struct virtio_pmem *vpmem = container_of(ws, struct virtio_pmem,
> > flush_work);
> > + struct bio *bio = vpmem->flush_bio;
> > +
> > + vpmem->start_flush = ktime_get_boottime();
> > + bio->bi_status =
> > errno_to_blk_status(virtio_pmem_flush(vpmem->nd_region));
> > + vpmem->prev_flush_start = vpmem->start_flush;
> > + vpmem->flush_bio = NULL;
> > + wake_up(&vpmem->sb_wait);
> > +
> > + /* Submit parent bio only for PREFLUSH */
> > + if (bio && (bio->bi_opf & REQ_PREFLUSH)) {
> > + bio->bi_opf &= ~REQ_PREFLUSH;
> > + submit_bio(bio);
> > + } else if (bio && (bio->bi_opf & REQ_FUA)) {
> > + bio->bi_opf &= ~REQ_FUA;
> > + bio_endio(bio);
> > + }
>
> Shouldn't the wait_event_lock_irq() be here rather than in
> async_pmem_flush()? That will cause the workqueue to back up and flush
> requests to coalesce.
but this is coalesced flush request
Re: [RFC v2 1/2] virtio-pmem: Async virtio-pmem flush
On Sun, Jul 25, 2021 at 11:09 PM Pankaj Gupta
wrote:
>
> From: Pankaj Gupta
>
> Implement asynchronous flush for virtio pmem using work queue
> to solve the preflush ordering issue. Also, coalesce the flush
> requests when a flush is already in process.
>
> Signed-off-by: Pankaj Gupta
> ---
> drivers/nvdimm/nd_virtio.c | 72
> drivers/nvdimm/virtio_pmem.c | 10 -
> drivers/nvdimm/virtio_pmem.h | 14 +++
> 3 files changed, 79 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
> index 10351d5b49fa..61b655b583be 100644
> --- a/drivers/nvdimm/nd_virtio.c
> +++ b/drivers/nvdimm/nd_virtio.c
> @@ -97,29 +97,69 @@ static int virtio_pmem_flush(struct nd_region *nd_region)
> return err;
> };
>
> +static void submit_async_flush(struct work_struct *ws);
> +
> /* The asynchronous flush callback function */
> int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
> {
> - /*
> -* Create child bio for asynchronous flush and chain with
> -* parent bio. Otherwise directly call nd_region flush.
> + /* queue asynchronous flush and coalesce the flush requests */
> + struct virtio_device *vdev = nd_region->provider_data;
> + struct virtio_pmem *vpmem = vdev->priv;
> + ktime_t req_start = ktime_get_boottime();
> +
> + spin_lock_irq(&vpmem->lock);
> + /* flush requests wait until ongoing flush completes,
> +* hence coalescing all the pending requests.
> */
> - if (bio && 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);
> - return 0;
> + wait_event_lock_irq(vpmem->sb_wait,
> + !vpmem->flush_bio ||
> + ktime_before(req_start, vpmem->prev_flush_start),
> + vpmem->lock);
> + /* new request after previous flush is completed */
> + if (ktime_after(req_start, vpmem->prev_flush_start)) {
> + WARN_ON(vpmem->flush_bio);
> + vpmem->flush_bio = bio;
> + bio = NULL;
> + }
Why the dance with ->prev_flush_start vs just calling queue_work()
again. queue_work() is naturally coalescing in that if the last work
request has not started execution another queue attempt will be
dropped.
> + spin_unlock_irq(&vpmem->lock);
> +
> + if (!bio) {
> + INIT_WORK(&vpmem->flush_work, submit_async_flush);
I expect this only needs to be initialized once at driver init time.
> + queue_work(vpmem->pmem_wq, &vpmem->flush_work);
> + return 1;
> + }
> +
> + /* flush completed in other context while we waited */
> + if (bio && (bio->bi_opf & REQ_PREFLUSH)) {
> + bio->bi_opf &= ~REQ_PREFLUSH;
> + submit_bio(bio);
> + } else if (bio && (bio->bi_opf & REQ_FUA)) {
> + bio->bi_opf &= ~REQ_FUA;
> + bio_endio(bio);
It's not clear to me how this happens, shouldn't all flush completions
be driven from the work completion?
> }
> - if (virtio_pmem_flush(nd_region))
> - return -EIO;
>
> return 0;
> };
> EXPORT_SYMBOL_GPL(async_pmem_flush);
> +
> +static void submit_async_flush(struct work_struct *ws)
> +{
> + struct virtio_pmem *vpmem = container_of(ws, struct virtio_pmem,
> flush_work);
> + struct bio *bio = vpmem->flush_bio;
> +
> + vpmem->start_flush = ktime_get_boottime();
> + bio->bi_status =
> errno_to_blk_status(virtio_pmem_flush(vpmem->nd_region));
> + vpmem->prev_flush_start = vpmem->start_flush;
> + vpmem->flush_bio = NULL;
> + wake_up(&vpmem->sb_wait);
> +
> + /* Submit parent bio only for PREFLUSH */
> + if (bio && (bio->bi_opf & REQ_PREFLUSH)) {
> + bio->bi_opf &= ~REQ_PREFLUSH;
> + submit_bio(bio);
> + } else if (bio && (bio->bi_opf & REQ_FUA)) {
> + bio->bi_opf &= ~REQ_FUA;
> + bio_endio(bio);
> + }
Shouldn't the wait_event_lock_irq() be here rather than in
async_pmem_flush()? That will cause the workqueue to back up and flush
requests to coalesce.
> +}
> MODULE_LICENSE("GPL");
> diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
> index 726c7354d465..56780a6140c7 100644
> --- a/drivers/nvdimm/virtio_pmem.c
> +++ b/drivers/nvdimm/virtio_pmem.c
> @@ -24,6 +24,7 @@ static int init_vq(struct virtio_pmem *vpmem)
> return PTR_ERR(vpmem->req_vq);
>
> spin_lock_init(&vpmem->pmem_lock);
> + spin_lock_init(&vpmem->lock);
Why 2 l
