ceph: perform asynchronous unlink if we have sufficient caps

The MDS is getting a new lock-caching facility that will allow it
to cache the necessary locks to allow asynchronous directory operations.
Since the CEPH_CAP_FILE_* caps are currently unused on directories,
we can repurpose those bits for this purpose.

When performing an unlink, if we have Fx on the parent directory,
and CEPH_CAP_DIR_UNLINK (aka Fr), and we know that the dentry being
removed is the primary link, then then we can fire off an unlink
request immediately and don't need to wait on reply before returning.

In that situation, just fix up the dcache and link count and return
immediately after issuing the call to the MDS. This does mean that we
need to hold an extra reference to the inode being unlinked, and extra
references to the caps to avoid races. Those references are put and
error handling is done in the r_callback routine.

If the operation ends up failing, then set a writeback error on the
directory inode, and the inode itself that can be fetched later by
an fsync on the dir.

The behavior of dir caps is slightly different from caps on normal
files. Because these are just considered an optimization, if the
session is reconnected, we will not automatically reclaim them. They
are instead considered lost until we do another synchronous op in the
parent directory.

Async dirops are enabled via the "nowsync" mount option, which is
patterned after the xfs "wsync" mount option. For now, the default
is "wsync", but eventually we may flip that.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index b1329cd5388a..c9784eb1159a 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -155,6 +155,7 @@ enum {
 	Opt_acl,
 	Opt_quotadf,
 	Opt_copyfrom,
+	Opt_wsync,
 };
 
 enum ceph_recover_session_mode {
@@ -194,6 +195,7 @@ static const struct fs_parameter_spec ceph_mount_parameters[] = {
 	fsparam_string	("snapdirname",			Opt_snapdirname),
 	fsparam_string	("source",			Opt_source),
 	fsparam_u32	("wsize",			Opt_wsize),
+	fsparam_flag_no	("wsync",			Opt_wsync),
 	{}
 };
 
@@ -444,6 +446,12 @@ static int ceph_parse_mount_param(struct fs_context *fc,
 			fc->sb_flags &= ~SB_POSIXACL;
 		}
 		break;
+	case Opt_wsync:
+		if (!result.negated)
+			fsopt->flags &= ~CEPH_MOUNT_OPT_ASYNC_DIROPS;
+		else
+			fsopt->flags |= CEPH_MOUNT_OPT_ASYNC_DIROPS;
+		break;
 	default:
 		BUG();
 	}
@@ -567,6 +575,9 @@ static int ceph_show_options(struct seq_file *m, struct dentry *root)
 	if (fsopt->flags & CEPH_MOUNT_OPT_CLEANRECOVER)
 		seq_show_option(m, "recover_session", "clean");
 
+	if (fsopt->flags & CEPH_MOUNT_OPT_ASYNC_DIROPS)
+		seq_puts(m, ",nowsync");
+
 	if (fsopt->wsize != CEPH_MAX_WRITE_SIZE)
 		seq_printf(m, ",wsize=%u", fsopt->wsize);
 	if (fsopt->rsize != CEPH_MAX_READ_SIZE)
@@ -1115,6 +1126,15 @@ static void ceph_free_fc(struct fs_context *fc)
 
 static int ceph_reconfigure_fc(struct fs_context *fc)
 {
+	struct ceph_parse_opts_ctx *pctx = fc->fs_private;
+	struct ceph_mount_options *fsopt = pctx->opts;
+	struct ceph_fs_client *fsc = ceph_sb_to_client(fc->root->d_sb);
+
+	if (fsopt->flags & CEPH_MOUNT_OPT_ASYNC_DIROPS)
+		ceph_set_mount_opt(fsc, ASYNC_DIROPS);
+	else
+		ceph_clear_mount_opt(fsc, ASYNC_DIROPS);
+
 	sync_filesystem(fc->root->d_sb);
 	return 0;
 }