NFS: Add a count of the number of unstable writes carried by an inode

In order to know when we should do opportunistic commits of the unstable
writes, when the VM is doing a background flush, we add a field to count
the number of unstable writes.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/inode.c

@@ -1404,6 +1404,7 @@ static void init_once(void *foo)
 	INIT_LIST_HEAD(&nfsi->access_cache_inode_lru);
 	INIT_RADIX_TREE(&nfsi->nfs_page_tree, GFP_ATOMIC);
 	nfsi->npages = 0;
+	nfsi->ncommit = 0;
 	atomic_set(&nfsi->silly_count, 1);
 	INIT_HLIST_HEAD(&nfsi->silly_list);
 	init_waitqueue_head(&nfsi->waitqueue);

fs/nfs/write.c

@@ -438,6 +438,7 @@ nfs_mark_request_commit(struct nfs_page *req)
 	radix_tree_tag_set(&nfsi->nfs_page_tree,
 			req->wb_index,
 			NFS_PAGE_TAG_COMMIT);
+	nfsi->ncommit++;
 	spin_unlock(&inode->i_lock);
 	inc_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
 	inc_bdi_stat(req->wb_page->mapping->backing_dev_info, BDI_RECLAIMABLE);
@@ -573,11 +574,15 @@ static int
 nfs_scan_commit(struct inode *inode, struct list_head *dst, pgoff_t idx_start, unsigned int npages)
 {
 	struct nfs_inode *nfsi = NFS_I(inode);
+	int ret;
 
 	if (!nfs_need_commit(nfsi))
 		return 0;
 
-	return nfs_scan_list(nfsi, dst, idx_start, npages, NFS_PAGE_TAG_COMMIT);
+	ret = nfs_scan_list(nfsi, dst, idx_start, npages, NFS_PAGE_TAG_COMMIT);
+	if (ret > 0)
+		nfsi->ncommit -= ret;
+	return ret;
 }
 #else
 static inline int nfs_need_commit(struct nfs_inode *nfsi)
@@ -642,9 +647,10 @@ static struct nfs_page *nfs_try_to_update_request(struct inode *inode,
 		spin_lock(&inode->i_lock);
 	}
 
-	if (nfs_clear_request_commit(req))
+	if (nfs_clear_request_commit(req) &&
 			radix_tree_tag_clear(&NFS_I(inode)->nfs_page_tree,
-				req->wb_index, NFS_PAGE_TAG_COMMIT);
+				req->wb_index, NFS_PAGE_TAG_COMMIT) != NULL)
+		NFS_I(inode)->ncommit--;
 
 	/* Okay, the request matches. Update the region */
 	if (offset < req->wb_offset) {

include/linux/nfs_fs.h

@@ -166,6 +166,7 @@ struct nfs_inode {
 	struct radix_tree_root	nfs_page_tree;
 
 	unsigned long		npages;
+	unsigned long		ncommit;
 
 	/* Open contexts for shared mmap writes */
 	struct list_head	open_files;