fuse: realloc page array

Writeback caching currently allocates requests with the maximum number of
possible pages, while the actual number of pages per request depends on a
couple of factors that cannot be determined when the request is allocated
(whether page is already under writeback, whether page is contiguous with
previous pages already added to a request).

This patch allows such requests to start with no page allocation (all pages
inline) and grow the page array on demand.

If the max_pages tunable remains the default value, then this will mean
just one allocation that is the same size as before.  If the tunable is
larger, then this adds at most 3 additional memory allocations (which is
generously compensated by the improved performance from the larger
request).

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 035843b501fe..f5507198ea00 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1827,7 +1827,13 @@ static int fuse_writepages_fill(struct page *page,
 	     data->orig_pages[req->num_pages - 1]->index + 1 != page->index)) {
 		fuse_writepages_send(data);
 		data->req = NULL;
+	} else if (req && req->num_pages == req->max_pages) {
+		if (!fuse_req_realloc_pages(fc, req, GFP_NOFS)) {
+			fuse_writepages_send(data);
+			req = data->req = NULL;
+		}
 	}
+
 	err = -ENOMEM;
 	tmp_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
 	if (!tmp_page)
@@ -1850,7 +1856,7 @@ static int fuse_writepages_fill(struct page *page,
 		struct fuse_inode *fi = get_fuse_inode(inode);
 
 		err = -ENOMEM;
-		req = fuse_request_alloc_nofs(fc->max_pages);
+		req = fuse_request_alloc_nofs(FUSE_REQ_INLINE_PAGES);
 		if (!req) {
 			__free_page(tmp_page);
 			goto out_unlock;