Re: [PATCH v14 101/138] iomap: Convert iomap_page_mkwrite to use a folio

[Darrick J. Wong]

On Thu, Jul 15, 2021 at 04:36:27AM +0100, Matthew Wilcox (Oracle) wrote:
> If we write to any page in a folio, we have to mark the entire
> folio as dirty, and potentially COW the entire folio, because it'll
> all get written back as one unit.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
>  fs/iomap/buffered-io.c | 42 +++++++++++++++++++++---------------------
>  1 file changed, 21 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 7c702d6c2f64..a3fe0d36c739 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -951,23 +951,23 @@ iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
>  }
>  EXPORT_SYMBOL_GPL(iomap_truncate_page);
>  
> -static loff_t
> -iomap_page_mkwrite_actor(struct inode *inode, loff_t pos, loff_t length,
> -		void *data, struct iomap *iomap, struct iomap *srcmap)
> +static loff_t iomap_folio_mkwrite_actor(struct inode *inode, loff_t pos,
> +		loff_t length, void *data, struct iomap *iomap,
> +		struct iomap *srcmap)
>  {
> -	struct page *page = data;
> -	struct folio *folio = page_folio(page);
> +	struct folio *folio = data;
>  	int ret;
>  
>  	if (iomap->flags & IOMAP_F_BUFFER_HEAD) {
> -		ret = __block_write_begin_int(page, pos, length, NULL, iomap);
> +		ret = __block_write_begin_int(&folio->page, pos, length, NULL,
> +						iomap);
>  		if (ret)
>  			return ret;
> -		block_commit_write(page, 0, length);
> +		block_commit_write(&folio->page, 0, length);
>  	} else {
> -		WARN_ON_ONCE(!PageUptodate(page));
> +		WARN_ON_ONCE(!folio_test_uptodate(folio));
>  		iomap_page_create(inode, folio);
> -		set_page_dirty(page);
> +		folio_mark_dirty(folio);
>  	}
>  
>  	return length;
> @@ -975,33 +975,33 @@ iomap_page_mkwrite_actor(struct inode *inode, loff_t pos, loff_t length,
>  
>  vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
>  {
> -	struct page *page = vmf->page;
> +	struct folio *folio = page_folio(vmf->page);

If before the page fault the folio was a compound 2M page, will the
memory manager will have split it into 4k pages before passing it to us?

That's a roundabout way of asking if we should expect folio_mkwrite at
some point. ;)

The conversion looks pretty straightforward though.

Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>

--D


>  	struct inode *inode = file_inode(vmf->vma->vm_file);
> -	unsigned long length;
> -	loff_t offset;
> +	size_t length;
> +	loff_t pos;
>  	ssize_t ret;
>  
> -	lock_page(page);
> -	ret = page_mkwrite_check_truncate(page, inode);
> +	folio_lock(folio);
> +	ret = folio_mkwrite_check_truncate(folio, inode);
>  	if (ret < 0)
>  		goto out_unlock;
>  	length = ret;
>  
> -	offset = page_offset(page);
> +	pos = folio_pos(folio);
>  	while (length > 0) {
> -		ret = iomap_apply(inode, offset, length,
> -				IOMAP_WRITE | IOMAP_FAULT, ops, page,
> -				iomap_page_mkwrite_actor);
> +		ret = iomap_apply(inode, pos, length,
> +				IOMAP_WRITE | IOMAP_FAULT, ops, folio,
> +				iomap_folio_mkwrite_actor);
>  		if (unlikely(ret <= 0))
>  			goto out_unlock;
> -		offset += ret;
> +		pos += ret;
>  		length -= ret;
>  	}
>  
> -	wait_for_stable_page(page);
> +	folio_wait_stable(folio);
>  	return VM_FAULT_LOCKED;
>  out_unlock:
> -	unlock_page(page);
> +	folio_unlock(folio);
>  	return block_page_mkwrite_return(ret);
>  }
>  EXPORT_SYMBOL_GPL(iomap_page_mkwrite);
> -- 
> 2.30.2
>