Re: [PATCH v5 3/7] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero

[Darrick J. Wong]

On Wed, May 12, 2021 at 01:37:24AM +0000, ruansy.fnst@xxxxxxxxxxx wrote:
> > -----Original Message-----
> > From: Darrick J. Wong <djwong@xxxxxxxxxx>
> > Subject: Re: [PATCH v5 3/7] fsdax: Add dax_iomap_cow_copy() for
> > dax_iomap_zero
> > 
> > On Tue, May 11, 2021 at 11:09:29AM +0800, Shiyang Ruan wrote:
> > > Punch hole on a reflinked file needs dax_copy_edge() too.  Otherwise,
> > > data in not aligned area will be not correct.  So, add the srcmap to
> > > dax_iomap_zero() and replace memset() as dax_copy_edge().
> > >
> > > Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> > > Reviewed-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
> > > ---
> > >  fs/dax.c               | 25 +++++++++++++++----------
> > >  fs/iomap/buffered-io.c |  2 +-
> > >  include/linux/dax.h    |  3 ++-
> > >  3 files changed, 18 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/fs/dax.c b/fs/dax.c
> > > index ef0e564e7904..ee9d28a79bfb 100644
> > > --- a/fs/dax.c
> > > +++ b/fs/dax.c
> > > @@ -1186,7 +1186,8 @@ static vm_fault_t dax_pmd_load_hole(struct
> > > xa_state *xas, struct vm_fault *vmf,  }  #endif /* CONFIG_FS_DAX_PMD
> > > */
> > >
> > > -s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
> > > +s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap,
> > > +		struct iomap *srcmap)
> > >  {
> > >  	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
> > >  	pgoff_t pgoff;
> > > @@ -1208,19 +1209,23 @@ s64 dax_iomap_zero(loff_t pos, u64 length,
> > > struct iomap *iomap)
> > >
> > >  	if (page_aligned)
> > >  		rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
> > > -	else
> > > +	else {
> > >  		rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
> > > -	if (rc < 0) {
> > > -		dax_read_unlock(id);
> > > -		return rc;
> > > -	}
> > > -
> > > -	if (!page_aligned) {
> > > -		memset(kaddr + offset, 0, size);
> > > +		if (rc < 0)
> > > +			goto out;
> > > +		if (iomap->addr != srcmap->addr) {
> > 
> > Why isn't this "if (srcmap->type != IOMAP_HOLE)" ?
> > 
> > I suppose it has the same effect, since @iomap should never be a hole and we
> > should never have a @srcmap that's the same as @iomap, but still, we use
> > IOMAP_HOLE checks in most other parts of fs/iomap/.
> 
> According to its caller `iomap_zero_range_actor()`, whether
> srcmap->type is IOMAP_HOLE has already been checked before
> `dax_iomap_zero()`.  So the check you suggested will always be true...

Ah right, so it is.  I'll go review the newest version of this patch.

--D

> 
> 
> --
> Thanks,
> Ruan Shiyang.
> 
> > 
> > Other than that, the logic looks decent to me.
> > 
> > --D
> > 
> > > +			rc = dax_iomap_cow_copy(offset, size, PAGE_SIZE, srcmap,
> > > +						kaddr);
> > > +			if (rc < 0)
> > > +				goto out;
> > > +		} else
> > > +			memset(kaddr + offset, 0, size);
> > >  		dax_flush(iomap->dax_dev, kaddr + offset, size);
> > >  	}
> > > +
> > > +out:
> > >  	dax_read_unlock(id);
> > > -	return size;
> > > +	return rc < 0 ? rc : size;
> > >  }
> > >
> > >  static loff_t
> > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index
> > > f2cd2034a87b..2734955ea67f 100644
> > > --- a/fs/iomap/buffered-io.c
> > > +++ b/fs/iomap/buffered-io.c
> > > @@ -933,7 +933,7 @@ static loff_t iomap_zero_range_actor(struct inode
> > *inode, loff_t pos,
> > >  		s64 bytes;
> > >
> > >  		if (IS_DAX(inode))
> > > -			bytes = dax_iomap_zero(pos, length, iomap);
> > > +			bytes = dax_iomap_zero(pos, length, iomap, srcmap);
> > >  		else
> > >  			bytes = iomap_zero(inode, pos, length, iomap, srcmap);
> > >  		if (bytes < 0)
> > > diff --git a/include/linux/dax.h b/include/linux/dax.h index
> > > b52f084aa643..3275e01ed33d 100644
> > > --- a/include/linux/dax.h
> > > +++ b/include/linux/dax.h
> > > @@ -237,7 +237,8 @@ vm_fault_t dax_finish_sync_fault(struct vm_fault
> > > *vmf,  int dax_delete_mapping_entry(struct address_space *mapping,
> > > pgoff_t index);  int dax_invalidate_mapping_entry_sync(struct
> > address_space *mapping,
> > >  				      pgoff_t index);
> > > -s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap);
> > > +s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap,
> > > +		struct iomap *srcmap);
> > >  static inline bool dax_mapping(struct address_space *mapping)  {
> > >  	return mapping->host && IS_DAX(mapping->host);
> > > --
> > > 2.31.1
> > >
> > >
> > >
> > 
>