RE: [PATCH v3 06/10] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero

ruansy.fnst
2021-04-01T07:02:27Z

> -----Original Message-----
> From: Ritesh Harjani <ritesh.list@gmail.com>
> Sent: Thursday, April 1, 2021 2:45 PM
> Subject: Re: [PATCH v3 06/10] fsdax: Add dax_iomap_cow_copy() for
> dax_iomap_zero
>
> On 21/03/19 09:52AM, 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@fujitsu.com>
> > ---
> > fs/dax.c | 9 +++++++--
> > fs/iomap/buffered-io.c | 2 +-
> > include/linux/dax.h | 3 ++-
> > 3 files changed, 10 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/dax.c b/fs/dax.c
> > index cfe513eb111e..348297b38f76 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -1174,7 +1174,8 @@ 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)
>
> Do we know why does dax_iomap_zero() operates on PAGE_SIZE range?
> IIUC, dax_zero_page_range() can take nr_pages as a parameter. But we still
> always use one page at a time. Why is that?

I think we can handle more than one page here. The length can be more than one PAGE_SIZE.

>
> > {
> > sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
> > pgoff_t pgoff;
> > @@ -1204,7 +1205,11 @@ s64 dax_iomap_zero(loff_t pos, u64 length, struct
> iomap *iomap)
> > }
> >
> > if (!page_aligned) {
> > - memset(kaddr + offset, 0, size);
> > + if (iomap->addr != srcmap->addr)
> > + dax_iomap_cow_copy(offset, size, PAGE_SIZE, srcmap,
> > + kaddr, true);
> > + else
> > + memset(kaddr + offset, 0, size);
> > dax_flush(iomap->dax_dev, kaddr + offset, size);
> > }
> > dax_read_unlock(id);
> >
>
> Maybe the above could be simplified to this?
>
> if (page_aligned) {
> rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
> } else {
> rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);

This looks good. Need add check for rc here.

> if (iomap->addr != srcmap->addr)
> dax_iomap_cow_copy(offset, size, PAGE_SIZE, srcmap,
> kaddr, true);
> else
> memset(kaddr + offset, 0, size);
> dax_flush(iomap->dax_dev, kaddr + offset, size);
> }
>
> dax_read_unlock(id);
> return rc < 0 ? rc : size;
>
> Other than that looks good.
> Feel free to add.
> Reviewed-by: Ritesh Harjani <ritesh.list@gmail.com>
>

--
Thanks,
Ruan Shiyang.