[PATCH] NFS: Make searching and waiting on busy writeback requests more efficient.

Basically copies the VFS's method for tracking writebacks and applies
it to the struct nfs_page.

Signed-off-by: Trond Myklebust <[e-mail]>

fs/nfs/pagelist.c

···
 }
 
 /**
+ * nfs_set_page_writeback_locked - Lock a request for writeback
+ * @req:
+ */
+int nfs_set_page_writeback_locked(struct nfs_page *req)
+{
+	struct nfs_inode *nfsi = NFS_I(req->wb_context->dentry->d_inode);
+
+	if (!nfs_lock_request(req))
+		return 0;
+	radix_tree_tag_set(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_WRITEBACK);
+	return 1;
+}
+
+/**
+ * nfs_clear_page_writeback - Unlock request and wake up sleepers
+ */
+void nfs_clear_page_writeback(struct nfs_page *req)
+{
+	struct nfs_inode *nfsi = NFS_I(req->wb_context->dentry->d_inode);
+
+	spin_lock(&nfsi->req_lock);
+	radix_tree_tag_clear(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_WRITEBACK);
+	spin_unlock(&nfsi->req_lock);
+	nfs_unlock_request(req);
+}
+
+/**
  * nfs_clear_request - Free up all resources allocated to the request
  * @req:
  *
···
 		if (req->wb_index > idx_end)
 			break;
 
-		if (!nfs_lock_request(req))
+		if (!nfs_set_page_writeback_locked(req))
 			continue;
 		nfs_list_remove_request(req);
 		nfs_list_add_request(req, dst);

fs/nfs/read.c

···
 	if (len < PAGE_CACHE_SIZE)
 		memclear_highpage_flush(page, len, PAGE_CACHE_SIZE - len);
 
-	nfs_lock_request(new);
 	nfs_list_add_request(new, &one_request);
 	nfs_pagein_one(&one_request, inode);
 	return 0;
···
 
 	nfs_clear_request(req);
 	nfs_release_request(req);
-	nfs_unlock_request(req);
 
 	dprintk("NFS: read done (%s/%Ld %d@%Ld)\n",
 			req->wb_context->dentry->d_inode->i_sb->s_id,
···
 	}
 	if (len < PAGE_CACHE_SIZE)
 		memclear_highpage_flush(page, len, PAGE_CACHE_SIZE - len);
-	nfs_lock_request(new);
 	nfs_list_add_request(new, desc->head);
 	return 0;
 }

fs/nfs/write.c

···
 
 	spin_lock(&nfsi->req_lock);
 	next = idx_start;
-	while (radix_tree_gang_lookup(&nfsi->nfs_page_tree, (void **)&req, next, 1)) {
+	while (radix_tree_gang_lookup_tag(&nfsi->nfs_page_tree, (void **)&req, next, 1, NFS_PAGE_TAG_WRITEBACK)) {
 		if (req->wb_index > idx_end)
 			break;
 
 		next = req->wb_index + 1;
-		if (!NFS_WBACK_BUSY(req))
-			continue;
+		BUG_ON(!NFS_WBACK_BUSY(req));
 
 		atomic_inc(&req->wb_count);
 		spin_unlock(&nfsi->req_lock);
···
 #else
 	nfs_inode_remove_request(req);
 #endif
-	nfs_unlock_request(req);
+	nfs_clear_page_writeback(req);
 }
 
 static inline int flush_task_priority(int how)
···
 		nfs_writedata_free(data);
 	}
 	nfs_mark_request_dirty(req);
-	nfs_unlock_request(req);
+	nfs_clear_page_writeback(req);
 	return -ENOMEM;
 }
 
···
 		struct nfs_page *req = nfs_list_entry(head->next);
 		nfs_list_remove_request(req);
 		nfs_mark_request_dirty(req);
-		nfs_unlock_request(req);
+		nfs_clear_page_writeback(req);
 	}
 	return -ENOMEM;
 }
···
 		req = nfs_list_entry(head->next);
 		nfs_list_remove_request(req);
 		nfs_mark_request_dirty(req);
-		nfs_unlock_request(req);
+		nfs_clear_page_writeback(req);
 	}
 	return error;
 }
···
 		nfs_inode_remove_request(req);
 #endif
 	next:
-		nfs_unlock_request(req);
+		nfs_clear_page_writeback(req);
 	}
 }
 
···
 		req = nfs_list_entry(head->next);
 		nfs_list_remove_request(req);
 		nfs_mark_request_commit(req);
-		nfs_unlock_request(req);
+		nfs_clear_page_writeback(req);
 	}
 	return -ENOMEM;
 }
···
 		dprintk(" mismatch\n");
 		nfs_mark_request_dirty(req);
 	next:
-		nfs_unlock_request(req);
+		nfs_clear_page_writeback(req);
 		res++;
 	}
 	sub_page_state(nr_unstable,res);

include/linux/nfs_page.h

···
 #include <asm/atomic.h>
 
 /*
+ * Valid flags for the radix tree
+ */
+#define NFS_PAGE_TAG_WRITEBACK	1
+
+/*
  * Valid flags for a dirty buffer
  */
 #define PG_BUSY			0
···
 				  unsigned int);
 extern  int nfs_wait_on_request(struct nfs_page *);
 extern	void nfs_unlock_request(struct nfs_page *req);
+extern  int nfs_set_page_writeback_locked(struct nfs_page *req);
+extern  void nfs_clear_page_writeback(struct nfs_page *req);
+
 
 /*
  * Lock the page of an asynchronous request without incrementing the wb_count
···
 {
 	if (list_empty(&req->wb_list))
 		return;
-	if (!NFS_WBACK_BUSY(req)) {
-		printk(KERN_ERR "NFS: unlocked request attempted removed from list!\n");
-		BUG();
-	}
 	list_del_init(&req->wb_list);
 	req->wb_list_head = NULL;
 }