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Date: Wed, 1 Apr 2020 12:14:16 -0400
From: Vivek Goyal <vgoyal@redhat.com>
To: Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v5 4/8] dax, pmem: Add a dax operation zero_page_range
Message-ID: <20200401161416.GC9398@redhat.com>
References: <20200218214841.10076-1-vgoyal@redhat.com>
 <20200218214841.10076-5-vgoyal@redhat.com>
 <CAPcyv4jKHxy5c8BZodePeCu5+Z=cwhtEfw3RnOD1ZDNob382bQ@mail.gmail.com>
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On Tue, Mar 31, 2020 at 12:38:16PM -0700, Dan Williams wrote:
> On Tue, Feb 18, 2020 at 1:49 PM Vivek Goyal <vgoyal@redhat.com> wrote:
> >
> > Add a dax operation zero_page_range, to zero a range of memory. This will
> > also clear any poison in the range being zeroed.
> >
> > As of now, zeroing of up to one page is allowed in a single call. There
> > are no callers which are trying to zero more than a page in a single call.
> > Once we grow the callers which zero more than a page in single call, we
> > can add that support. Primary reason for not doing that yet is that this
> > will add little complexity in dm implementation where a range might be
> > spanning multiple underlying targets and one will have to split the range
> > into multiple sub ranges and call zero_page_range() on individual targets.
> >
> > Suggested-by: Christoph Hellwig <hch@infradead.org>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > ---
> >  drivers/dax/super.c   | 19 +++++++++++++++++++
> >  drivers/nvdimm/pmem.c | 10 ++++++++++
> >  include/linux/dax.h   |  3 +++
> >  3 files changed, 32 insertions(+)
> >
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index 0aa4b6bc5101..c912808bc886 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -344,6 +344,25 @@ size_t dax_copy_to_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
> >  }
> >  EXPORT_SYMBOL_GPL(dax_copy_to_iter);
> >
> > +int dax_zero_page_range(struct dax_device *dax_dev, u64 offset, size_t len)
> > +{
> > +       if (!dax_alive(dax_dev))
> > +               return -ENXIO;
> > +
> > +       if (!dax_dev->ops->zero_page_range)
> > +               return -EOPNOTSUPP;
> 
> This seems too late to be doing the validation. It would be odd for
> random filesystem operations to see this error. I would move the check
> to alloc_dax() and fail that if the caller fails to implement the
> operation.
> 
> An incremental patch on top to fix this up would be ok. Something like
> "Now that all dax_operations providers implement zero_page_range()
> mandate it at alloc_dax time".

Hi Dan,

Posted an extra patch in same patch series for this.

https://lore.kernel.org/linux-fsdevel/20200228163456.1587-1-vgoyal@redhat.com/T/#m624680cbb5e714266d4b34ade2d6c390dae69598

Vivek
> 
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Date:   Wed, 1 Apr 2020 12:14:16 -0400
From:   Vivek Goyal <vgoyal@redhat.com>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-nvdimm <linux-nvdimm@lists.01.org>,
        Christoph Hellwig <hch@infradead.org>,
        device-mapper development <dm-devel@redhat.com>,
        Vishal L Verma <vishal.l.verma@intel.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v5 4/8] dax, pmem: Add a dax operation zero_page_range
Message-ID: <20200401161416.GC9398@redhat.com>
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 <20200218214841.10076-5-vgoyal@redhat.com>
 <CAPcyv4jKHxy5c8BZodePeCu5+Z=cwhtEfw3RnOD1ZDNob382bQ@mail.gmail.com>
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On Tue, Mar 31, 2020 at 12:38:16PM -0700, Dan Williams wrote:
> On Tue, Feb 18, 2020 at 1:49 PM Vivek Goyal <vgoyal@redhat.com> wrote:
> >
> > Add a dax operation zero_page_range, to zero a range of memory. This will
> > also clear any poison in the range being zeroed.
> >
> > As of now, zeroing of up to one page is allowed in a single call. There
> > are no callers which are trying to zero more than a page in a single call.
> > Once we grow the callers which zero more than a page in single call, we
> > can add that support. Primary reason for not doing that yet is that this
> > will add little complexity in dm implementation where a range might be
> > spanning multiple underlying targets and one will have to split the range
> > into multiple sub ranges and call zero_page_range() on individual targets.
> >
> > Suggested-by: Christoph Hellwig <hch@infradead.org>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > ---
> >  drivers/dax/super.c   | 19 +++++++++++++++++++
> >  drivers/nvdimm/pmem.c | 10 ++++++++++
> >  include/linux/dax.h   |  3 +++
> >  3 files changed, 32 insertions(+)
> >
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index 0aa4b6bc5101..c912808bc886 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -344,6 +344,25 @@ size_t dax_copy_to_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
> >  }
> >  EXPORT_SYMBOL_GPL(dax_copy_to_iter);
> >
> > +int dax_zero_page_range(struct dax_device *dax_dev, u64 offset, size_t len)
> > +{
> > +       if (!dax_alive(dax_dev))
> > +               return -ENXIO;
> > +
> > +       if (!dax_dev->ops->zero_page_range)
> > +               return -EOPNOTSUPP;
> 
> This seems too late to be doing the validation. It would be odd for
> random filesystem operations to see this error. I would move the check
> to alloc_dax() and fail that if the caller fails to implement the
> operation.
> 
> An incremental patch on top to fix this up would be ok. Something like
> "Now that all dax_operations providers implement zero_page_range()
> mandate it at alloc_dax time".

Hi Dan,

Posted an extra patch in same patch series for this.

https://lore.kernel.org/linux-fsdevel/20200228163456.1587-1-vgoyal@redhat.com/T/#m624680cbb5e714266d4b34ade2d6c390dae69598

Vivek
>