[PATCH 4/6] fuse: rework fuse_readpages()

[Maxim Patlasov <mpatlasov@parallels.com>]

The patch uses 'nr_pages' argument of fuse_readpages() as the heuristics for
number of page pointers to allocate.

This can be improved further by taking in consideration fc->max_read and gaps
between page indices, but it's not clear wheteher it's worthy or not.
---
 fs/fuse/file.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index c811f3d..9a6dcc6 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -641,6 +641,7 @@ struct fuse_fill_data {
 	struct fuse_req *req;
 	struct file *file;
 	struct inode *inode;
+	unsigned nr_pages;
 };
 
 static int fuse_readpages_fill(void *_data, struct page *page)
@@ -656,8 +657,10 @@ static int fuse_readpages_fill(void *_data, struct page *page)
 	    (req->num_pages == FUSE_MAX_PAGES_PER_REQ ||
 	     (req->num_pages + 1) * PAGE_CACHE_SIZE > fc->max_read ||
 	     req->pages[req->num_pages - 1]->index + 1 != page->index)) {
+		int nr_alloc = min_t(unsigned, data->nr_pages,
+				     FUSE_MAX_PAGES_PER_REQ);
 		fuse_send_readpages(req, data->file);
-		data->req = req = fuse_get_req_multipage(fc, FUSE_MAX_PAGES_PER_REQ);
+		data->req = req = fuse_get_req_multipage(fc, nr_alloc);
 		if (IS_ERR(req)) {
 			unlock_page(page);
 			return PTR_ERR(req);
@@ -666,6 +669,7 @@ static int fuse_readpages_fill(void *_data, struct page *page)
 	page_cache_get(page);
 	req->pages[req->num_pages] = page;
 	req->num_pages++;
+	data->nr_pages--;
 	return 0;
 }
 
@@ -676,6 +680,7 @@ static int fuse_readpages(struct file *file, struct address_space *mapping,
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct fuse_fill_data data;
 	int err;
+	int nr_alloc = min_t(unsigned, nr_pages, FUSE_MAX_PAGES_PER_REQ);
 
 	err = -EIO;
 	if (is_bad_inode(inode))
@@ -683,7 +688,8 @@ static int fuse_readpages(struct file *file, struct address_space *mapping,
 
 	data.file = file;
 	data.inode = inode;
-	data.req = fuse_get_req_multipage(fc, FUSE_MAX_PAGES_PER_REQ);
+	data.req = fuse_get_req_multipage(fc, nr_alloc);
+	data.nr_pages = nr_pages;
 	err = PTR_ERR(data.req);
 	if (IS_ERR(data.req))
 		goto out;