Re: [PATCH 15/15] gfs2: use iomap for buffered I/O in ordered and writeback mode

[Christoph Hellwig <hch@infradead.org>]

On Tue, Dec 10, 2019 at 11:19:38AM +0100, Andreas Gruenbacher wrote:
> @@ -75,13 +75,12 @@ static int gfs2_unstuffer_page(struct gfs2_inode *ip, struct buffer_head *dibh,
>  		memcpy(kaddr, dibh->b_data + sizeof(struct gfs2_dinode), dsize);
>  		memset(kaddr + dsize, 0, PAGE_SIZE - dsize);
>  		kunmap(page);
> -
> -		SetPageUptodate(page);
>  	}
>  
>  	if (gfs2_is_jdata(ip)) {
>  		struct buffer_head *bh;
>  
> +		SetPageUptodate(page);
>  		if (!page_has_buffers(page))
>  			create_empty_buffers(page, BIT(inode->i_blkbits),
>  					     BIT(BH_Uptodate));
> @@ -93,6 +92,9 @@ static int gfs2_unstuffer_page(struct gfs2_inode *ip, struct buffer_head *dibh,
>  		set_buffer_uptodate(bh);
>  		gfs2_trans_add_data(ip->i_gl, bh);
>  	} else {
> +		iomap_page_create(inode, page);
> +		iomap_set_range_uptodate(page, 0, i_blocksize(inode));
> +		set_page_dirty(page);
>  		gfs2_ordered_add_inode(ip);
>  	}

Can you create a helper that copies the data from a passed in kernel
pointer, length pair into the page, then marks it uptodate and dirty,
please?

> @@ -555,6 +555,8 @@ static vm_fault_t gfs2_page_mkwrite(struct vm_fault *vmf)
>  out_uninit:
>  	gfs2_holder_uninit(&gh);
>  	if (ret == 0) {
> +		if (!gfs2_is_jdata(ip))
> +			iomap_page_create(inode, page);

What is this one for?  The iomap_page is supposed to use lazy
allocation, that is we only allocate it once it is used.  What code
expects the structure but doesn't see it without this hunk?  I
guess it is iomap_writepage_map, which should probably just switch
to call iomap_page_create.

That being said is there any way we can get gfs2 to use
iomap_page_mkwrite for the !jdata case?