linux-kernel - Re: [PATCH 32/32] NFS: Convert readpage to readahead and use netfs

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Date:   Tue, 26 Jan 2021 01:36:11 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Dave Wysochanski <dwysocha@...hat.com>,
        Jeff Layton <jlayton@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 32/32] NFS: Convert readpage to readahead and use
 netfs_readahead for fscache


For Subject: s/readpage/readpages/

On Mon, Jan 25, 2021 at 09:37:29PM +0000, David Howells wrote:
> +int __nfs_readahead_from_fscache(struct nfs_readdesc *desc,
> +				 struct readahead_control *rac)

I thought you wanted it called ractl instead of rac?  That's what I've
been using in new code.

> -	dfprintk(FSCACHE, "NFS: nfs_getpages_from_fscache (0x%p/%u/0x%p)\n",
> -		 nfs_i_fscache(inode), npages, inode);
> +	dfprintk(FSCACHE, "NFS: nfs_readahead_from_fscache (0x%p/0x%p)\n",
> +		 nfs_i_fscache(inode), inode);

We do have readahead_count() if this is useful information to be logging.

> +static inline int nfs_readahead_from_fscache(struct nfs_readdesc *desc,
> +					     struct readahead_control *rac)
>  {
> -	if (NFS_I(inode)->fscache)
> -		return __nfs_readpages_from_fscache(ctx, inode, mapping, pages,
> -						    nr_pages);
> +	if (NFS_I(rac->mapping->host)->fscache)
> +		return __nfs_readahead_from_fscache(desc, rac);
>  	return -ENOBUFS;
>  }

Not entirely sure that it's worth having the two functions separated any more.

>  	/* attempt to read as many of the pages as possible from the cache
>  	 * - this returns -ENOBUFS immediately if the cookie is negative
>  	 */
> -	ret = nfs_readpages_from_fscache(desc.ctx, inode, mapping,
> -					 pages, &nr_pages);
> +	ret = nfs_readahead_from_fscache(&desc, rac);
>  	if (ret == 0)
>  		goto read_complete; /* all pages were read */
>  
>  	nfs_pageio_init_read(&desc.pgio, inode, false,
>  			     &nfs_async_read_completion_ops);
>  
> -	ret = read_cache_pages(mapping, pages, readpage_async_filler, &desc);
> +	while ((page = readahead_page(rac))) {
> +		ret = readpage_async_filler(&desc, page);
> +		put_page(page);
> +	}

I thought with the new API we didn't need to do this kind of thing
any more?  ie no matter whether fscache is configured in or not, it'll
submit the I/Os.