linux-kernel - Re: [PATCH v3 5/6] netfs, 9p, afs, ceph: Use folios

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Date:   Wed, 3 Nov 2021 14:21:17 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Jeff Layton <jlayton@...nel.org>,
        Marc Dionne <marc.dionne@...istor.com>,
        Ilya Dryomov <idryomov@...il.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        v9fs-developer@...ts.sourceforge.net,
        linux-afs@...ts.infradead.org, ceph-devel@...r.kernel.org,
        linux-cachefs@...hat.com, linux-fsdevel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        devel@...ts.orangefs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/6] netfs, 9p, afs, ceph: Use folios

On Tue, Nov 02, 2021 at 08:31:14AM +0000, David Howells wrote:
> -static int v9fs_vfs_writepage_locked(struct page *page)
> +static int v9fs_vfs_write_folio_locked(struct folio *folio)
>  {
> -	struct inode *inode = page->mapping->host;
> +	struct inode *inode = folio_inode(folio);
>  	struct v9fs_inode *v9inode = V9FS_I(inode);
> -	loff_t start = page_offset(page);
> +	loff_t start = folio_pos(folio);
>  	loff_t size = i_size_read(inode);
>  	struct iov_iter from;
> -	int err, len;
> +	size_t gran = folio_size(folio), len;
> +	int err;
>  
> -	if (page->index == size >> PAGE_SHIFT)
> -		len = size & ~PAGE_MASK;
> -	else
> -		len = PAGE_SIZE;
> +	len = (size >= start + gran) ? gran : size - start;

This seems like the most complicated way to write this ... how about:

        size_t len = min_t(loff_t, isize - start, folio_size(folio));

> @@ -322,23 +322,24 @@ static void afs_req_issue_op(struct netfs_read_subrequest *subreq)
>  
>  static int afs_symlink_readpage(struct file *file, struct page *page)
>  {
> -	struct afs_vnode *vnode = AFS_FS_I(page->mapping->host);
> +	struct afs_vnode *vnode = AFS_FS_I(page_mapping(page)->host);

How does swap end up calling readpage on a symlink?

>  	ret = afs_fetch_data(fsreq->vnode, fsreq);
> -	page_endio(page, false, ret);
> +	page_endio(&folio->page, false, ret);

We need a folio_endio() ...

>  int afs_write_end(struct file *file, struct address_space *mapping,
>  		  loff_t pos, unsigned len, unsigned copied,
> -		  struct page *page, void *fsdata)
> +		  struct page *subpage, void *fsdata)
>  {
> +	struct folio *folio = page_folio(subpage);
>  	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
>  	unsigned long priv;
> -	unsigned int f, from = pos & (thp_size(page) - 1);
> +	unsigned int f, from = pos & (folio_size(folio) - 1);

Isn't that:

	size_t from = offset_in_folio(folio, pos);

(not that i think we're getting folios larger than 4GB any time soon,
but it'd be nice to be prepared for it)