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

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Message-ID: <D6C85B77-17CA-4BA6-9C2C-C63A8AF613AB@oracle.com>
Date:   Tue, 26 Jan 2021 15:24:31 +0000
From:   Chuck Lever <chuck.lever@...cle.com>
To:     Matthew Wilcox <willy@...radead.org>,
        David Howells <dhowells@...hat.com>,
        Dave Wysochanski <dwysocha@...hat.com>
CC:     Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-cachefs <linux-cachefs@...hat.com>,
        "linux-afs@...ts.infradead.org" <linux-afs@...ts.infradead.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        CIFS <linux-cifs@...r.kernel.org>,
        "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
        "v9fs-developer@...ts.sourceforge.net" 
        <v9fs-developer@...ts.sourceforge.net>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 32/32] NFS: Convert readpage to readahead and use
 netfs_readahead for fscache



> On Jan 25, 2021, at 8:36 PM, Matthew Wilcox <willy@...radead.org> wrote:
> 
> 
> 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.

As a sidebar, the Linux NFS community is transitioning to tracepoints.
It would be helpful (but not completely necessary) to use tracepoints
in new code instead of printk.


>> +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.

--
Chuck Lever