Re: [PATCH 2/9] fs: Introduce i_blocks_per_page

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

On Mon, Aug 24, 2020 at 03:55:03PM +0100, Matthew Wilcox (Oracle) wrote:
> This helper is useful for both THPs and for supporting block size larger
> than page size.  Convert all users that I could find (we have a few
> different ways of writing this idiom, and I may have missed some).
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

/me wonders what will happen when someone tries to make blocksz >
pagesize work, but as the most likely someone already rvb'd this I guess
it's fine:

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/iomap/buffered-io.c  |  8 ++++----
>  fs/jfs/jfs_metapage.c   |  2 +-
>  fs/xfs/xfs_aops.c       |  2 +-
>  include/linux/pagemap.h | 16 ++++++++++++++++
>  4 files changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index cffd575e57b6..13d5cdab8dcd 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -46,7 +46,7 @@ iomap_page_create(struct inode *inode, struct page *page)
>  {
>  	struct iomap_page *iop = to_iomap_page(page);
>  
> -	if (iop || i_blocksize(inode) == PAGE_SIZE)
> +	if (iop || i_blocks_per_page(inode, page) <= 1)
>  		return iop;
>  
>  	iop = kmalloc(sizeof(*iop), GFP_NOFS | __GFP_NOFAIL);
> @@ -147,7 +147,7 @@ iomap_iop_set_range_uptodate(struct page *page, unsigned off, unsigned len)
>  	unsigned int i;
>  
>  	spin_lock_irqsave(&iop->uptodate_lock, flags);
> -	for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {
> +	for (i = 0; i < i_blocks_per_page(inode, page); i++) {
>  		if (i >= first && i <= last)
>  			set_bit(i, iop->uptodate);
>  		else if (!test_bit(i, iop->uptodate))
> @@ -1078,7 +1078,7 @@ iomap_finish_page_writeback(struct inode *inode, struct page *page,
>  		mapping_set_error(inode->i_mapping, -EIO);
>  	}
>  
> -	WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE && !iop);
> +	WARN_ON_ONCE(i_blocks_per_page(inode, page) > 1 && !iop);
>  	WARN_ON_ONCE(iop && atomic_read(&iop->write_count) <= 0);
>  
>  	if (!iop || atomic_dec_and_test(&iop->write_count))
> @@ -1374,7 +1374,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
>  	int error = 0, count = 0, i;
>  	LIST_HEAD(submit_list);
>  
> -	WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE && !iop);
> +	WARN_ON_ONCE(i_blocks_per_page(inode, page) > 1 && !iop);
>  	WARN_ON_ONCE(iop && atomic_read(&iop->write_count) != 0);
>  
>  	/*
> diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
> index a2f5338a5ea1..176580f54af9 100644
> --- a/fs/jfs/jfs_metapage.c
> +++ b/fs/jfs/jfs_metapage.c
> @@ -473,7 +473,7 @@ static int metapage_readpage(struct file *fp, struct page *page)
>  	struct inode *inode = page->mapping->host;
>  	struct bio *bio = NULL;
>  	int block_offset;
> -	int blocks_per_page = PAGE_SIZE >> inode->i_blkbits;
> +	int blocks_per_page = i_blocks_per_page(inode, page);
>  	sector_t page_start;	/* address of page in fs blocks */
>  	sector_t pblock;
>  	int xlen;
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index b35611882ff9..55d126d4e096 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -544,7 +544,7 @@ xfs_discard_page(
>  			page, ip->i_ino, offset);
>  
>  	error = xfs_bmap_punch_delalloc_range(ip, start_fsb,
> -			PAGE_SIZE / i_blocksize(inode));
> +			i_blocks_per_page(inode, page));
>  	if (error && !XFS_FORCED_SHUTDOWN(mp))
>  		xfs_alert(mp, "page discard unable to remove delalloc mapping.");
>  out_invalidate:
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 7de11dcd534d..853733286138 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -899,4 +899,20 @@ static inline int page_mkwrite_check_truncate(struct page *page,
>  	return offset;
>  }
>  
> +/**
> + * i_blocks_per_page - How many blocks fit in this page.
> + * @inode: The inode which contains the blocks.
> + * @page: The page (head page if the page is a THP).
> + *
> + * If the block size is larger than the size of this page, return zero.
> + *
> + * Context: The caller should hold a refcount on the page to prevent it
> + * from being split.
> + * Return: The number of filesystem blocks covered by this page.
> + */
> +static inline
> +unsigned int i_blocks_per_page(struct inode *inode, struct page *page)
> +{
> +	return thp_size(page) >> inode->i_blkbits;
> +}
>  #endif /* _LINUX_PAGEMAP_H */
> -- 
> 2.28.0
>