However ... something else occurs to me.  We could use the bdi congestion
markers to guide the timeout.
When the wait for PG_private times out, or when a connection re-establishment
is required (and maybe other similar times) we could set_bdi_congested().
Then in nfs_release_page() we could completely avoid the wait if
bdi_write_congested().

The congestion setting should encourage vmscan away from the filesystem so it
won't keep calling nfs_release_page() which is a bonus.

Setting bdi_congestion from the RPC layer might be awkward from a layering
perspective, but probably isn't necessary.

Would the following allay your concerns?  The change to
nfs_inode_remove_request ensures that any congestion is removed when a
'commit' completes.

We certainly could keep the PF_FSTRANS setting in the SUNRPC layer - that was
why it was a separate patch.  It would be nice to find a uniform solution
though.

Thanks,
NeilBrown

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 5949ca37cd18..bc674ad250ce 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c

@@ -477,10 +477,15 @@ static int nfs_release_page(struct page *page, gfp_t gfp)
         * benefit that someone else can worry about the freezer.
         */
        if (mapping) {
+               struct nfs_server *nfss = NFS_SERVER(mapping->host);
                nfs_commit_inode(mapping->host, 0);
-               if ((gfp & __GFP_WAIT))
+               if ((gfp & __GFP_WAIT) &&
+                   !bdi_write_congested(&nfss->backing_dev_info))
                        wait_on_page_bit_killable_timeout(page, PG_private,
                                                          HZ);
+               if (PagePrivate(page))
+                       set_bdi_congested(&nfss->backing_dev_info,
+                                         BLK_RW_ASYNC);
        }
        /* If PagePrivate() is set, then the page is not freeable */
        if (PagePrivate(page))

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 700e7a865e6d..3ab122e92c9d 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c

@@ -726,6 +726,7 @@ static void nfs_inode_remove_request(struct nfs_page *req)
        struct inode *inode = req->wb_context->dentry->d_inode;
        struct nfs_inode *nfsi = NFS_I(inode);
        struct nfs_page *head;
+       struct nfs_server *nfss = NFS_SERVER(inode);

        if (nfs_page_group_sync_on_bit(req, PG_REMOVE)) {
                head = req->wb_head;

@@ -742,6 +743,9 @@ static void nfs_inode_remove_request(struct nfs_page *req)
                spin_unlock(&inode->i_lock);
        }

+       if (atomic_long_read(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)
+               clear_bdi_congested(&nfss->backing_dev_info, BLK_RW_ASYNC);