NFS: avoid waiting at all in nfs_release_page when congested.

If nfs_release_page() is called on a sequence of pages which are all
in the same file which is blocked on COMMIT, each page could
contribute a 1 second delay which could be come excessive.  I have
seen delays of as much as 208 seconds.

To keep the delay to one second, mark the bdi as write-congested
if the commit didn't finished.  Once it does finish, the
write-congested flag will be cleared by nfs_commit_release_pages().

With this, the longest total delay in try_to_free_pages that I have
seen is under 3 seconds.  With no waiting in nfs_release_page at all
I have seen delays of nearly 1.5 seconds.

Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index c063a4e70354..12493846a2d3 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1611,6 +1611,7 @@ static void nfs_commit_release_pages(struct nfs_commit_data *data)
         struct nfs_page *req;
         int status = data->task.tk_status;
         struct nfs_commit_info cinfo;
+        struct nfs_server *nfss;
 
         while (!list_empty(&data->pages)) {
                 req = nfs_list_entry(data->pages.next);
@@ -1644,6 +1645,10 @@ static void nfs_commit_release_pages(struct nfs_commit_data *data)
         next:
                 nfs_unlock_and_release_request(req);
         }
+        nfss = NFS_SERVER(data->inode);
+        if (atomic_long_read(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)
+                clear_bdi_congested(&nfss->backing_dev_info, BLK_RW_ASYNC);
+
         nfs_init_cinfo(&cinfo, data->inode, data->dreq);
         if (atomic_dec_and_test(&cinfo.mds->rpcs_out))
                 nfs_commit_clear_lock(NFS_I(data->inode));