NFS: Use cond_resched_lock() to reduce latencies in the commit scans

Ensure that we conditionally drop the inode->i_lock when it is safe
to do so in the commit loops.
We do so after locking the nfs_page, but before removing it from the
commit list. We can then use list_safe_reset_next to recover the loop
after the lock is retaken.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 628d9a69d0a2..bd93d40099f9 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -561,7 +561,8 @@ nfs_need_commit(struct nfs_inode *nfsi)
 
 /* i_lock held by caller */
 static int
-nfs_scan_commit_list(struct list_head *src, struct list_head *dst, int max)
+nfs_scan_commit_list(struct list_head *src, struct list_head *dst, int max,
+                spinlock_t *lock)
 {
         struct nfs_page *req, *tmp;
         int ret = 0;
@@ -569,6 +570,8 @@ nfs_scan_commit_list(struct list_head *src, struct list_head *dst, int max)
         list_for_each_entry_safe(req, tmp, src, wb_list) {
                 if (!nfs_lock_request(req))
                         continue;
+                if (cond_resched_lock(lock))
+                        list_safe_reset_next(req, tmp, wb_list);
                 nfs_request_remove_commit_list(req);
                 nfs_list_add_request(req, dst);
                 ret++;
@@ -596,8 +599,10 @@ nfs_scan_commit(struct inode *inode, struct list_head *dst)
         if (nfsi->ncommit > 0) {
                 const int max = INT_MAX;
 
-                ret = nfs_scan_commit_list(&nfsi->commit_list, dst, max);
-                ret += pnfs_scan_commit_lists(inode, max - ret);
+                ret = nfs_scan_commit_list(&nfsi->commit_list, dst, max,
+                                &inode->i_lock);
+                ret += pnfs_scan_commit_lists(inode, max - ret,
+                                &inode->i_lock);
         }
         spin_unlock(&inode->i_lock);
         return ret;