fuse: optimize __fuse_direct_io()

__fuse_direct_io() allocates fuse-requests by calling fuse_get_req(fc, n). The
patch calculates 'n' based on iov[] array. This is useful because allocating
FUSE_MAX_PAGES_PER_REQ page pointers and descriptors for each fuse request
would be waste of memory in case of iov-s of smaller size.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 21 insertions, 4 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index b2aa6c21e209..68e10d43bd3f 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1088,14 +1088,14 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
                 return 0;
         }
 
-        while (nbytes < *nbytesp && req->num_pages < FUSE_MAX_PAGES_PER_REQ) {
+        while (nbytes < *nbytesp && req->num_pages < req->max_pages) {
                 unsigned npages;
                 unsigned long user_addr = fuse_get_user_addr(ii);
                 unsigned offset = user_addr & ~PAGE_MASK;
                 size_t frag_size = fuse_get_frag_size(ii, *nbytesp - nbytes);
                 int ret;
 
-                unsigned n = FUSE_MAX_PAGES_PER_REQ - req->num_pages;
+                unsigned n = req->max_pages - req->num_pages;
                 frag_size = min_t(size_t, frag_size, n << PAGE_SHIFT);
 
                 npages = (frag_size + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
@@ -1131,6 +1131,23 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
         return 0;
 }
 
+static inline int fuse_iter_npages(const struct iov_iter *ii_p)
+{
+        struct iov_iter ii = *ii_p;
+        int npages = 0;
+
+        while (iov_iter_count(&ii) && npages < FUSE_MAX_PAGES_PER_REQ) {
+                unsigned long user_addr = fuse_get_user_addr(&ii);
+                unsigned offset = user_addr & ~PAGE_MASK;
+                size_t frag_size = iov_iter_single_seg_count(&ii);
+
+                npages += (frag_size + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
+                iov_iter_advance(&ii, frag_size);
+        }
+
+        return min(npages, FUSE_MAX_PAGES_PER_REQ);
+}
+
 static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
                                 unsigned long nr_segs, size_t count,
                                 loff_t *ppos, int write)
@@ -1145,7 +1162,7 @@ static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
 
         iov_iter_init(&ii, iov, nr_segs, count, 0);
 
-        req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+        req = fuse_get_req(fc, fuse_iter_npages(&ii));
         if (IS_ERR(req))
                 return PTR_ERR(req);
 
@@ -1180,7 +1197,7 @@ static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
                         break;
                 if (count) {
                         fuse_put_request(fc, req);
-                        req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+                        req = fuse_get_req(fc, fuse_iter_npages(&ii));
                         if (IS_ERR(req))
                                 break;
                 }