When flushing a lot of caps to the MDS's at once (e.g. for syncfs),
we can end up waiting a substantial amount of time for MDS replies, due
to the fact that it may delay some of them so that it can batch them up
together in a single journal transaction. This can lead to stalls when
calling sync or syncfs.
What we'd really like to do is request expedited service on the _last_
cap we're flushing back to the server. If the CHECK_CAPS_FLUSH flag is
set on the request and the current inode was the last one on the
session->s_cap_dirty list, then mark the request with
CEPH_CLIENT_CAPS_SYNC.
Note that this heuristic is not perfect. New inodes can race onto the
list after we've started flushing, but it does seem to fix some common
use cases.
Reported-by: Jan Fajerski <jfajerski@xxxxxxxx>
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
fs/ceph/caps.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 95c9b25e45a6..3630f05993b3 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1987,6 +1987,7 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
}
for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
+ int mflags = 0;
struct cap_msg_args arg;
cap = rb_entry(p, struct ceph_cap, ci_node);
@@ -2118,6 +2119,9 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
flushing = ci->i_dirty_caps;
flush_tid = __mark_caps_flushing(inode, session, false,
&oldest_flush_tid);
+ if (flags & CHECK_CAPS_FLUSH &&
+ list_empty(&session->s_cap_dirty))
+ mflags |= CEPH_CLIENT_CAPS_SYNC;
} else {
flushing = 0;
flush_tid = 0;
@@ -2128,8 +2132,8 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
mds = cap->mds; /* remember mds, so we don't repeat */
- __prep_cap(&arg, cap, CEPH_CAP_OP_UPDATE, 0, cap_used, want,
- retain, flushing, flush_tid, oldest_flush_tid);
+ __prep_cap(&arg, cap, CEPH_CAP_OP_UPDATE, mflags, cap_used,
+ want, retain, flushing, flush_tid, oldest_flush_tid);
spin_unlock(&ci->i_ceph_lock);
__send_cap(mdsc, &arg, ci);
--
2.25.1
