[PATCH v3 4/7] s390,dcssblk,dax: Add dax zero_page_range operation to dcssblk driver

[PATCH v3 4/7] s390,dcssblk,dax: Add dax zero_page_range operation to dcssblk driver

[Vivek Goyal]

Add dax operation zero_page_range for dcssblk driver.

CC: linux-s390@vger.kernel.org
Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
 drivers/s390/block/dcssblk.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
index 63502ca537eb..331abab5d066 100644
--- a/drivers/s390/block/dcssblk.c
+++ b/drivers/s390/block/dcssblk.c
@@ -57,11 +57,28 @@ static size_t dcssblk_dax_copy_to_iter(struct dax_device *dax_dev,
 	return copy_to_iter(addr, bytes, i);
 }
 
+static int dcssblk_dax_zero_page_range(struct dax_device *dax_dev, u64 offset,
+				       size_t len)
+{
+	long rc;
+	void *kaddr;
+	pgoff_t pgoff = offset >> PAGE_SHIFT;
+	unsigned page_offset = offset_in_page(offset);
+
+	rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr, NULL);
+	if (rc < 0)
+		return rc;
+	memset(kaddr + page_offset, 0, len);
+	dax_flush(dax_dev, kaddr + page_offset, len);
+	return 0;
+}
+
 static const struct dax_operations dcssblk_dax_ops = {
 	.direct_access = dcssblk_dax_direct_access,
 	.dax_supported = generic_fsdax_supported,
 	.copy_from_iter = dcssblk_dax_copy_from_iter,
 	.copy_to_iter = dcssblk_dax_copy_to_iter,
+	.zero_page_range = dcssblk_dax_zero_page_range,
 };
 
 struct dcssblk_dev_info {
-- 
2.20.1

Re: [PATCH v3 4/7] s390,dcssblk,dax: Add dax zero_page_range operation to dcssblk driver

[Gerald Schaefer]

On Fri,  7 Feb 2020 15:26:49 -0500
Vivek Goyal <vgoyal@redhat.com> wrote:

> Add dax operation zero_page_range for dcssblk driver.
> 
> CC: linux-s390@vger.kernel.org
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> ---
>  drivers/s390/block/dcssblk.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
> index 63502ca537eb..331abab5d066 100644
> --- a/drivers/s390/block/dcssblk.c
> +++ b/drivers/s390/block/dcssblk.c
> @@ -57,11 +57,28 @@ static size_t dcssblk_dax_copy_to_iter(struct dax_device *dax_dev,
>  	return copy_to_iter(addr, bytes, i);
>  }
>  
> +static int dcssblk_dax_zero_page_range(struct dax_device *dax_dev, u64 offset,
> +				       size_t len)
> +{
> +	long rc;
> +	void *kaddr;
> +	pgoff_t pgoff = offset >> PAGE_SHIFT;
> +	unsigned page_offset = offset_in_page(offset);
> +
> +	rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr, NULL);

Why do you pass only 1 page as nr_pages argument for dax_direct_access()?
In some other patch in this series there is a comment that this will
currently only be used for one page, but support for more pages might be
added later. Wouldn't it make sense to rather use something like
PAGE_ALIGN(page_offset + len) >> PAGE_SHIFT instead of 1 here, so that
this won't have to be changed when callers will be ready to use it
with more than one page?

Of course, I guess then we'd also need some check on the return value
from dax_direct_access(), i.e. if the returned available range is
large enough for the requested range.

Re: [PATCH v3 4/7] s390,dcssblk,dax: Add dax zero_page_range operation to dcssblk driver

[Vivek Goyal]

On Mon, Feb 10, 2020 at 09:53:15PM +0100, Gerald Schaefer wrote:
> On Fri,  7 Feb 2020 15:26:49 -0500
> Vivek Goyal <vgoyal@redhat.com> wrote:
> 
> > Add dax operation zero_page_range for dcssblk driver.
> > 
> > CC: linux-s390@vger.kernel.org
> > Suggested-by: Christoph Hellwig <hch@infradead.org>
> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > ---
> >  drivers/s390/block/dcssblk.c | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> > 
> > diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
> > index 63502ca537eb..331abab5d066 100644
> > --- a/drivers/s390/block/dcssblk.c
> > +++ b/drivers/s390/block/dcssblk.c
> > @@ -57,11 +57,28 @@ static size_t dcssblk_dax_copy_to_iter(struct dax_device *dax_dev,
> >  	return copy_to_iter(addr, bytes, i);
> >  }
> >  
> > +static int dcssblk_dax_zero_page_range(struct dax_device *dax_dev, u64 offset,
> > +				       size_t len)
> > +{
> > +	long rc;
> > +	void *kaddr;
> > +	pgoff_t pgoff = offset >> PAGE_SHIFT;
> > +	unsigned page_offset = offset_in_page(offset);
> > +
> > +	rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr, NULL);
> 
> Why do you pass only 1 page as nr_pages argument for dax_direct_access()?
> In some other patch in this series there is a comment that this will
> currently only be used for one page, but support for more pages might be
> added later. Wouldn't it make sense to rather use something like
> PAGE_ALIGN(page_offset + len) >> PAGE_SHIFT instead of 1 here, so that
> this won't have to be changed when callers will be ready to use it
> with more than one page?
> 
> Of course, I guess then we'd also need some check on the return value
> from dax_direct_access(), i.e. if the returned available range is
> large enough for the requested range.

I left it at 1 page because that's the current limitation of this
interface and there are no callers which are zeroing across page
boundaries.

I prefer to keep it this way and modify it when we are extending this
interface to allow zeroing across page boundaries. Because even if I add
that logic, I can't test it.

But if you still prefer to change it, I am open to make that change.

Thanks
Vivek

Re: [PATCH v3 4/7] s390,dcssblk,dax: Add dax zero_page_range operation to dcssblk driver

[Gerald Schaefer]

On Tue, 11 Feb 2020 10:11:14 -0500
Vivek Goyal <vgoyal@redhat.com> wrote:

> On Mon, Feb 10, 2020 at 09:53:15PM +0100, Gerald Schaefer wrote:
> > On Fri,  7 Feb 2020 15:26:49 -0500
> > Vivek Goyal <vgoyal@redhat.com> wrote:
> > 
> > > Add dax operation zero_page_range for dcssblk driver.
> > > 
> > > CC: linux-s390@vger.kernel.org
> > > Suggested-by: Christoph Hellwig <hch@infradead.org>
> > > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > > ---
> > >  drivers/s390/block/dcssblk.c | 17 +++++++++++++++++
> > >  1 file changed, 17 insertions(+)
> > > 
> > > diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
> > > index 63502ca537eb..331abab5d066 100644
> > > --- a/drivers/s390/block/dcssblk.c
> > > +++ b/drivers/s390/block/dcssblk.c
> > > @@ -57,11 +57,28 @@ static size_t dcssblk_dax_copy_to_iter(struct dax_device *dax_dev,
> > >  	return copy_to_iter(addr, bytes, i);
> > >  }
> > >  
> > > +static int dcssblk_dax_zero_page_range(struct dax_device *dax_dev, u64 offset,
> > > +				       size_t len)
> > > +{
> > > +	long rc;
> > > +	void *kaddr;
> > > +	pgoff_t pgoff = offset >> PAGE_SHIFT;
> > > +	unsigned page_offset = offset_in_page(offset);
> > > +
> > > +	rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr, NULL);
> > 
> > Why do you pass only 1 page as nr_pages argument for dax_direct_access()?
> > In some other patch in this series there is a comment that this will
> > currently only be used for one page, but support for more pages might be
> > added later. Wouldn't it make sense to rather use something like
> > PAGE_ALIGN(page_offset + len) >> PAGE_SHIFT instead of 1 here, so that
> > this won't have to be changed when callers will be ready to use it
> > with more than one page?
> > 
> > Of course, I guess then we'd also need some check on the return value
> > from dax_direct_access(), i.e. if the returned available range is
> > large enough for the requested range.
> 
> I left it at 1 page because that's the current limitation of this
> interface and there are no callers which are zeroing across page
> boundaries.
> 
> I prefer to keep it this way and modify it when we are extending this
> interface to allow zeroing across page boundaries. Because even if I add
> that logic, I can't test it.

OK, fine with me.

Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>