11:11 a.m.
On 10:46 21/05, Darrick J. Wong wrote:
On Mon, Apr 29, 2019 at 12:26:39PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn(a)suse.com>
>
> Change dax_iomap_pfn to return the address as well in order to
> use it for performing a memcpy in case the type is IOMAP_DAX_COW.
> We don't handle PMD because btrfs does not support hugepages.
>
> Question:
> The sequence of bdev_dax_pgoff() and dax_direct_access() is
> used multiple times to calculate address and pfn's. Would it make
> sense to call it while calculating address as well to reduce code?
>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn(a)suse.com>
> ---
> fs/dax.c | 19 +++++++++++++++----
> 1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 610bfa861a28..718b1632a39d 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -984,7 +984,7 @@ static sector_t dax_iomap_sector(struct iomap *iomap, loff_t
pos)
> }
>
> static int dax_iomap_pfn(struct iomap *iomap, loff_t pos, size_t size,
> - pfn_t *pfnp)
> + pfn_t *pfnp, void **addr)
> {
> const sector_t sector = dax_iomap_sector(iomap, pos);
> pgoff_t pgoff;
> @@ -996,7 +996,7 @@ static int dax_iomap_pfn(struct iomap *iomap, loff_t pos, size_t
size,
> return rc;
> id = dax_read_lock();
> length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size),
> - NULL, pfnp);
> + addr, pfnp);
> if (length < 0) {
> rc = length;
> goto out;
> @@ -1286,6 +1286,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf,
pfn_t *pfnp,
> XA_STATE(xas, &mapping->i_pages, vmf->pgoff);
> struct inode *inode = mapping->host;
> unsigned long vaddr = vmf->address;
> + void *addr;
> loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
> struct iomap iomap = { 0 };
Ugh, I had forgotten that fs/dax.c open-codes iomap_apply, probably
because the actor returns vm_fault_t, not bytes copied. I guess that
makes it a tiny bit more complicated to pass in two (struct iomap *) to
the iomap_begin function...
I am not sure I understand this. We do not use iomap_apply() in
the fault path: dax_iomap_pte_fault(). We just use iomap_begin()
and iomap_end(). So, why can we not implement your idea of using two
iomaps? What does open-coding iomap-apply mean?
--
Goldwyn