From: Trond Myklebust <trond.myklebust@primarydata.com>
Date: Mon, 17 Jul 2017 13:30:13 +0000 (-0400)
Subject: NFS: Reduce lock contention in nfs_page_find_head_request()
X-Git-Tag: MMI-PSA29.97-13-9~4705^2~17^2~29
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=82749dd4efcec8e90fa7769eec3dd0afa2e3396a;p=GitHub%2FMotorolaMobilityLLC%2Fkernel-slsi.git

NFS: Reduce lock contention in nfs_page_find_head_request()

Add a lockless check for whether or not the page might be carrying
an existing writeback before we grab the inode->i_lock.

Reported-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
---

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 1d447e37f472..06e150c4e315 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -190,9 +190,11 @@ static struct nfs_page *nfs_page_find_head_request(struct page *page)
 	struct inode *inode = page_file_mapping(page)->host;
 	struct nfs_page *req = NULL;
 
-	spin_lock(&inode->i_lock);
-	req = nfs_page_find_head_request_locked(NFS_I(inode), page);
-	spin_unlock(&inode->i_lock);
+	if (PagePrivate(page) || PageSwapCache(page)) {
+		spin_lock(&inode->i_lock);
+		req = nfs_page_find_head_request_locked(NFS_I(inode), page);
+		spin_unlock(&inode->i_lock);
+	}
 	return req;
 }