On Thu, Dec 01, 2022 at 03:28:54PM +0000, Shiyang Ruan wrote:
> If a dax page is shared, mapread at different offsets can also trigger
> page fault on same dax page. So, change the flag from "cow" to
> "shared". And get the shared flag from filesystem when read.
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
Makes sense.
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> ---
> fs/dax.c | 19 +++++++------------
> fs/xfs/xfs_iomap.c | 2 +-
> 2 files changed, 8 insertions(+), 13 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 6b6e07ad8d80..f1eb59bee0b5 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -846,12 +846,6 @@ static bool dax_fault_is_synchronous(const struct iomap_iter *iter,
> (iter->iomap.flags & IOMAP_F_DIRTY);
> }
>
> -static bool dax_fault_is_cow(const struct iomap_iter *iter)
> -{
> - return (iter->flags & IOMAP_WRITE) &&
> - (iter->iomap.flags & IOMAP_F_SHARED);
> -}
> -
> /*
> * 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
> @@ -865,13 +859,14 @@ static void *dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
> {
> struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> void *new_entry = dax_make_entry(pfn, flags);
> - bool dirty = !dax_fault_is_synchronous(iter, vmf->vma);
> - bool cow = dax_fault_is_cow(iter);
> + bool write = iter->flags & IOMAP_WRITE;
> + bool dirty = write && !dax_fault_is_synchronous(iter, vmf->vma);
> + bool shared = iter->iomap.flags & IOMAP_F_SHARED;
>
> if (dirty)
> __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
>
> - if (cow || (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE))) {
> + if (shared || (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE))) {
> unsigned long index = xas->xa_index;
> /* we are replacing a zero page with block mapping */
> if (dax_is_pmd_entry(entry))
> @@ -883,12 +878,12 @@ static void *dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
>
> xas_reset(xas);
> xas_lock_irq(xas);
> - if (cow || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> + if (shared || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> void *old;
>
> dax_disassociate_entry(entry, mapping, false);
> dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address,
> - cow);
> + shared);
> /*
> * Only swap our new entry into the page cache if the current
> * entry is a zero page or an empty entry. If a normal PTE or
> @@ -908,7 +903,7 @@ static void *dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
> if (dirty)
> xas_set_mark(xas, PAGECACHE_TAG_DIRTY);
>
> - if (cow)
> + if (write && shared)
> xas_set_mark(xas, PAGECACHE_TAG_TOWRITE);
>
> xas_unlock_irq(xas);
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index 07da03976ec1..881de99766ca 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -1215,7 +1215,7 @@ xfs_read_iomap_begin(
> return error;
> error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap,
> &nimaps, 0);
> - if (!error && (flags & IOMAP_REPORT))
> + if (!error && ((flags & IOMAP_REPORT) || IS_DAX(inode)))
> error = xfs_reflink_trim_around_shared(ip, &imap, &shared);
> xfs_iunlock(ip, lockmode);
>
> --
> 2.38.1
>
