NFS: fix subtle change in COMMIT behavior

Recent work in the pgio layer made it possible for there to be more than one
request per page. This caused a subtle change in commit behavior, because
write.c:nfs_commit_unstable_pages compares the number of *pages* waiting for
writeback against the number of requests on a commit list to choose when to
send a COMMIT in a non-blocking flush.

This is probably hard to hit in normal operation - you have to be using
rsize/wsize < PAGE_SIZE, or pnfs with lots of boundaries that are not page
aligned to have a noticeable change in behavior.

Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index f83b02d..d489ff3 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -670,7 +670,8 @@ static void nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
 	nfs_lock_request(req);
 
 	spin_lock(&inode->i_lock);
-	if (!nfsi->npages && NFS_PROTO(inode)->have_delegation(inode, FMODE_WRITE))
+	if (!nfsi->nrequests &&
+	    NFS_PROTO(inode)->have_delegation(inode, FMODE_WRITE))
 		inode->i_version++;
 	/*
 	 * Swap-space should not get truncated. Hence no need to plug the race
@@ -681,9 +682,11 @@ static void nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
 		SetPagePrivate(req->wb_page);
 		set_page_private(req->wb_page, (unsigned long)req);
 	}
-	nfsi->npages++;
+	nfsi->nrequests++;
 	/* this a head request for a page group - mark it as having an
-	 * extra reference so sub groups can follow suit */
+	 * extra reference so sub groups can follow suit.
+	 * This flag also informs pgio layer when to bump nrequests when
+	 * adding subrequests. */
 	WARN_ON(test_and_set_bit(PG_INODE_REF, &req->wb_flags));
 	kref_get(&req->wb_kref);
 	spin_unlock(&inode->i_lock);
@@ -709,7 +712,11 @@ static void nfs_inode_remove_request(struct nfs_page *req)
 			wake_up_page(head->wb_page, PG_private);
 			clear_bit(PG_MAPPED, &head->wb_flags);
 		}
-		nfsi->npages--;
+		nfsi->nrequests--;
+		spin_unlock(&inode->i_lock);
+	} else {
+		spin_lock(&inode->i_lock);
+		nfsi->nrequests--;
 		spin_unlock(&inode->i_lock);
 	}
 
@@ -1735,7 +1742,7 @@ static int nfs_commit_unstable_pages(struct inode *inode, struct writeback_contr
 		/* Don't commit yet if this is a non-blocking flush and there
 		 * are a lot of outstanding writes for this mapping.
 		 */
-		if (nfsi->commit_info.ncommit <= (nfsi->npages >> 1))
+		if (nfsi->commit_info.ncommit <= (nfsi->nrequests >> 1))
 			goto out_mark_dirty;
 
 		/* don't wait for the COMMIT response */