Re: [PATCH v10 24/25] fuse: Convert from readpages to readahead

From: Matthew Wilcox <willy@infradead.org>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org,
	linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com,
	ocfs2-devel@oss.oracle.com, linux-xfs <linux-xfs@vger.kernel.org>,
	Dave Chinner <dchinner@redhat.com>,
	William Kucharski <william.kucharski@oracle.com>
Subject: Re: [PATCH v10 24/25] fuse: Convert from readpages to readahead
Date: Wed, 25 Mar 2020 05:02:54 -0700
Message-ID: <20200325120254.GA22483@bombadil.infradead.org> (raw)
In-Reply-To: <CAJfpegu7EFcWrg3bP+-2BX_kb52RrzBCo_U3QKYzUkZfe4EjDA@mail.gmail.com>

On Wed, Mar 25, 2020 at 10:42:56AM +0100, Miklos Szeredi wrote:
> > +       while ((page = readahead_page(rac))) {
> > +               if (fuse_readpages_fill(&data, page) != 0)
> 
> Shouldn't this unlock + put page on error?

We're certainly inconsistent between the two error exits from
fuse_readpages_fill().  But I think we can simplify the whole thing
... how does this look to you?

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 5749505bcff6..57ea9a364e62 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -915,76 +915,32 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file)
 	fuse_readpages_end(fc, &ap->args, err);
 }
 
-struct fuse_fill_data {
-	struct fuse_io_args *ia;
-	struct file *file;
-	struct inode *inode;
-	unsigned int nr_pages;
-	unsigned int max_pages;
-};
-
-static int fuse_readpages_fill(struct fuse_fill_data *data, struct page *page)
-{
-	struct fuse_io_args *ia = data->ia;
-	struct fuse_args_pages *ap = &ia->ap;
-	struct inode *inode = data->inode;
-	struct fuse_conn *fc = get_fuse_conn(inode);
-
-	fuse_wait_on_page_writeback(inode, page->index);
-
-	if (ap->num_pages &&
-	    (ap->num_pages == fc->max_pages ||
-	     (ap->num_pages + 1) * PAGE_SIZE > fc->max_read ||
-	     ap->pages[ap->num_pages - 1]->index + 1 != page->index)) {
-		data->max_pages = min_t(unsigned int, data->nr_pages,
-					fc->max_pages);
-		fuse_send_readpages(ia, data->file);
-		data->ia = ia = fuse_io_alloc(NULL, data->max_pages);
-		if (!ia)
-			return -ENOMEM;
-		ap = &ia->ap;
-	}
-
-	if (WARN_ON(ap->num_pages >= data->max_pages)) {
-		unlock_page(page);
-		fuse_io_free(ia);
-		return -EIO;
-	}
-
-	ap->pages[ap->num_pages] = page;
-	ap->descs[ap->num_pages].length = PAGE_SIZE;
-	ap->num_pages++;
-	data->nr_pages--;
-	return 0;
-}
-
 static void fuse_readahead(struct readahead_control *rac)
 {
 	struct inode *inode = rac->mapping->host;
 	struct fuse_conn *fc = get_fuse_conn(inode);
-	struct fuse_fill_data data;
-	struct page *page;
 
 	if (is_bad_inode(inode))
 		return;
 
-	data.file = rac->file;
-	data.inode = inode;
-	data.nr_pages = readahead_count(rac);
-	data.max_pages = min_t(unsigned int, data.nr_pages, fc->max_pages);
-	data.ia = fuse_io_alloc(NULL, data.max_pages);
-	if (!data.ia)
-		return;
+	while (readahead_count(rac)) {
+		struct fuse_io_args *ia;
+		struct fuse_args_pages *ap;
+		unsigned int i, nr_pages;
 
-	while ((page = readahead_page(rac))) {
-		if (fuse_readpages_fill(&data, page) != 0)
+		nr_pages = min(readahead_count(rac), fc->max_pages);
+		ia = fuse_io_alloc(NULL, nr_pages);
+		if (!ia)
 			return;
+		ap = &ia->ap;
+		__readahead_batch(rac, ap->pages, nr_pages);
+		for (i = 0; i < nr_pages; i++) {
+			fuse_wait_on_page_writeback(inode, ap->pages[i]->index);
+			ap->descs[i].length = PAGE_SIZE;
+		}
+		ap->num_pages = nr_pages;
+		fuse_send_readpages(ia, rac->file);
 	}
-
-	if (data.ia->ap.num_pages)
-		fuse_send_readpages(data.ia, rac->file);
-	else
-		fuse_io_free(data.ia);
 }
 
 static ssize_t fuse_cache_read_iter(struct kiocb *iocb, struct iov_iter *to)
