On Sun, Aug 15, 2021 at 11:05 PM Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx> wrote:
>
> We replace the existing entry to the newly allocated one in case of CoW.
> Also, we mark the entry as PAGECACHE_TAG_TOWRITE so writeback marks this
> entry as writeprotected. This helps us snapshots so new write
> pagefaults after snapshots trigger a CoW.
>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Reviewed-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
> Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> ---
> fs/dax.c | 39 ++++++++++++++++++++++++++++-----------
> 1 file changed, 28 insertions(+), 11 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 697a7b7bb96f..e49ba68cc7e4 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -734,6 +734,10 @@ static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_d
> return 0;
> }
>
> +/* DAX Insert Flag: The state of the entry we insert */
> +#define DAX_IF_DIRTY (1 << 0)
> +#define DAX_IF_COW (1 << 1)
> +
> /*
> * By this point grab_mapping_entry() has ensured that we have a locked entry
> * of the appropriate size so we don't have to worry about downgrading PMDs to
> @@ -741,16 +745,19 @@ static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_d
> * already in the tree, we will skip the insertion and just dirty the PMD as
> * appropriate.
> */
> -static void *dax_insert_entry(struct xa_state *xas,
> - struct address_space *mapping, struct vm_fault *vmf,
> - void *entry, pfn_t pfn, unsigned long flags, bool dirty)
> +static void *dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
> + void *entry, pfn_t pfn, unsigned long flags,
> + unsigned int insert_flags)
I'm late, so feel free to ignore this style feedback, but what about
changing the signature to:
static void *dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
const struct iomap_iter *iter, void
*entry, pfn_t pfn,
unsigned long flags)
> {
> + struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> void *new_entry = dax_make_entry(pfn, flags);
> + bool dirty = insert_flags & DAX_IF_DIRTY;
> + bool cow = insert_flags & DAX_IF_COW;
...and then calculate these flags from the source data. I'm just
reacting to "yet more flags".
So, take it or leave it,
Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
