fuse: rework fuse_retrieve()

The patch reworks fuse_retrieve() to allocate only so many page pointers
as needed. The core part of the patch is the following calculation:

	num_pages = (num + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;

(thanks Miklos for formula). All other changes are mostly shuffling lines.

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

1 files changed, 15 insertions, 10 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ff5e8bed5d88..28d9792de4a2 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1577,13 +1577,24 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
         unsigned int num;
         unsigned int offset;
         size_t total_len = 0;
+        int num_pages;
 
-        req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+        offset = outarg->offset & ~PAGE_CACHE_MASK;
+        file_size = i_size_read(inode);
+
+        num = outarg->size;
+        if (outarg->offset > file_size)
+                num = 0;
+        else if (outarg->offset + num > file_size)
+                num = file_size - outarg->offset;
+
+        num_pages = (num + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
+        num_pages = min(num_pages, FUSE_MAX_PAGES_PER_REQ);
+
+        req = fuse_get_req(fc, num_pages);
         if (IS_ERR(req))
                 return PTR_ERR(req);
 
-        offset = outarg->offset & ~PAGE_CACHE_MASK;
-
         req->in.h.opcode = FUSE_NOTIFY_REPLY;
         req->in.h.nodeid = outarg->nodeid;
         req->in.numargs = 2;
@@ -1592,14 +1603,8 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
         req->end = fuse_retrieve_end;
 
         index = outarg->offset >> PAGE_CACHE_SHIFT;
-        file_size = i_size_read(inode);
-        num = outarg->size;
-        if (outarg->offset > file_size)
-                num = 0;
-        else if (outarg->offset + num > file_size)
-                num = file_size - outarg->offset;
 
-        while (num && req->num_pages < FUSE_MAX_PAGES_PER_REQ) {
+        while (num && req->num_pages < num_pages) {
                 struct page *page;
                 unsigned int this_num;