Re: [PATCH 05/14] iomap: Support THPs in invalidatepage

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Oct 14, 2020 at 04:03:48AM +0100, Matthew Wilcox (Oracle) wrote:
> If we're punching a hole in a THP, we need to remove the per-page
> iomap data as the THP is about to be split and each page will need
> its own.  This means that writepage can now come across a page with
> no iop allocated, so remove the assertion that there is already one,
> and just create one (with the uptodate bits set) if there isn't one.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  fs/iomap/buffered-io.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 95ac66731297..4633ebd03a3f 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -60,6 +60,8 @@ iomap_page_create(struct inode *inode, struct page *page)
>  	iop = kzalloc(struct_size(iop, uptodate, BITS_TO_LONGS(nr_blocks)),
>  			GFP_NOFS | __GFP_NOFAIL);
>  	spin_lock_init(&iop->uptodate_lock);
> +	if (PageUptodate(page))
> +		bitmap_fill(iop->uptodate, nr_blocks);
>  	attach_page_private(page, iop);
>  	return iop;
>  }
> @@ -494,10 +496,14 @@ iomap_invalidatepage(struct page *page, unsigned int offset, unsigned int len)
>  	 * If we are invalidating the entire page, clear the dirty state from it
>  	 * and release it to avoid unnecessary buildup of the LRU.
>  	 */
> -	if (offset == 0 && len == PAGE_SIZE) {
> +	if (offset == 0 && len == thp_size(page)) {
>  		WARN_ON_ONCE(PageWriteback(page));
>  		cancel_dirty_page(page);
>  		iomap_page_release(page);
> +	} else if (PageTransHuge(page)) {
> +		/* Punching a hole in a THP requires releasing the iop */
> +		WARN_ON_ONCE(!PageUptodate(page) && PageDirty(page));
> +		iomap_page_release(page);
>  	}
>  }
>  EXPORT_SYMBOL_GPL(iomap_invalidatepage);
> @@ -1363,14 +1369,13 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
>  		struct writeback_control *wbc, struct inode *inode,
>  		struct page *page, u64 end_offset)
>  {
> -	struct iomap_page *iop = to_iomap_page(page);
> +	struct iomap_page *iop = iomap_page_create(inode, page);
>  	struct iomap_ioend *ioend, *next;
>  	unsigned len = i_blocksize(inode);
>  	u64 file_offset; /* file offset of page */
>  	int error = 0, count = 0, i;
>  	LIST_HEAD(submit_list);
>  
> -	WARN_ON_ONCE(i_blocks_per_page(inode, page) > 1 && !iop);
>  	WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) != 0);
>  
>  	/*
> @@ -1415,7 +1420,6 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
>  			 */
>  			if (wpc->ops->discard_page)
>  				wpc->ops->discard_page(page);
> -			ClearPageUptodate(page);

Er, I don't get it -- why do we now leave the page up to date after
writeback fails?

--D

>  			unlock_page(page);
>  			goto done;
>  		}
> -- 
> 2.28.0
>