On Mon, 2021-07-05 at 09:22 +0800, xiubli@xxxxxxxxxx wrote:
> From: Xiubo Li <xiubli@xxxxxxxxxx>
>
> For the client requests who will have unsafe and safe replies from
> MDS daemons, in the MDS side the MDS daemons won't flush the mdlog
> (journal log) immediatelly, because they think it's unnecessary.
> That's true for most cases but not all, likes the fsync request.
> The fsync will wait until all the unsafe replied requests to be
> safely replied.
>
> Normally if there have multiple threads or clients are running, the
> whole mdlog in MDS daemons could be flushed in time if any request
> will trigger the mdlog submit thread. So usually we won't experience
> the normal operations will stuck for a long time. But in case there
> has only one client with only thread is running, the stuck phenomenon
> maybe obvious and the worst case it must wait at most 5 seconds to
> wait the mdlog to be flushed by the MDS's tick thread periodically.
>
> This patch will trigger to flush the mdlog in the relevant and auth
> MDSes to which the in-flight requests are sent just before waiting
> the unsafe requests to finish.
>
> Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
> ---
> fs/ceph/caps.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 78 insertions(+)
>
> diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
> index c6a3352a4d52..4b966c29d9b5 100644
> --- a/fs/ceph/caps.c
> +++ b/fs/ceph/caps.c
> @@ -2286,6 +2286,7 @@ static int caps_are_flushed(struct inode *inode, u64 flush_tid)
> */
> static int unsafe_request_wait(struct inode *inode)
> {
> + struct ceph_mds_client *mdsc = ceph_sb_to_client(inode->i_sb)->mdsc;
> struct ceph_inode_info *ci = ceph_inode(inode);
> struct ceph_mds_request *req1 = NULL, *req2 = NULL;
> int ret, err = 0;
> @@ -2305,6 +2306,82 @@ static int unsafe_request_wait(struct inode *inode)
> }
> spin_unlock(&ci->i_unsafe_lock);
>
> + /*
> + * Trigger to flush the journal logs in all the relevant MDSes
> + * manually, or in the worst case we must wait at most 5 seconds
> + * to wait the journal logs to be flushed by the MDSes periodically.
> + */
> + if (req1 || req2) {
> + struct ceph_mds_session **sessions = NULL;
> + struct ceph_mds_session *s;
> + struct ceph_mds_request *req;
> + unsigned int max;
> + int i;
> +
> + /*
> + * The mdsc->max_sessions is unlikely to be changed
> + * mostly, here we will retry it by reallocating the
> + * sessions arrary memory to get rid of the mdsc->mutex
> + * lock.
> + */
> +retry:
> + max = mdsc->max_sessions;
> + sessions = krealloc(sessions, max * sizeof(s), __GFP_ZERO);
The kerneldoc over krealloc() says:
* The contents of the object pointed to are preserved up to the
* lesser of the new and old sizes (__GFP_ZERO flag is effectively
ignored).
This code however relies on krealloc zeroing out the new part of the
allocation. Do you know for certain that that works?
> + if (!sessions) {
> + err = -ENOMEM;
> + goto out;
> + }
> + spin_lock(&ci->i_unsafe_lock);
> + if (req1) {
> + list_for_each_entry(req, &ci->i_unsafe_dirops,
> + r_unsafe_dir_item) {
> + s = req->r_session;
> + if (unlikely(s->s_mds > max)) {
> + spin_unlock(&ci->i_unsafe_lock);
> + goto retry;
> + }
> + if (!sessions[s->s_mds]) {
> + s = ceph_get_mds_session(s);
> + sessions[s->s_mds] = s;
nit: maybe just do:
sessions[s->s_mds] = ceph_get_mds_session(s);
> + }
> + }
> + }
> + if (req2) {
> + list_for_each_entry(req, &ci->i_unsafe_iops,
> + r_unsafe_target_item) {
> + s = req->r_session;
> + if (unlikely(s->s_mds > max)) {
> + spin_unlock(&ci->i_unsafe_lock);
> + goto retry;
> + }
> + if (!sessions[s->s_mds]) {
> + s = ceph_get_mds_session(s);
> + sessions[s->s_mds] = s;
> + }
> + }
> + }
> + spin_unlock(&ci->i_unsafe_lock);
> +
> + /* the auth MDS */
> + spin_lock(&ci->i_ceph_lock);
> + if (ci->i_auth_cap) {
> + s = ci->i_auth_cap->session;
> + if (!sessions[s->s_mds])
> + sessions[s->s_mds] = ceph_get_mds_session(s);
> + }
> + spin_unlock(&ci->i_ceph_lock);
> +
> + /* send flush mdlog request to MDSes */
> + for (i = 0; i < max; i++) {
> + s = sessions[i];
> + if (s) {
> + send_flush_mdlog(s);
> + ceph_put_mds_session(s);
> + }
> + }
> + kfree(sessions);
> + }
> +
> dout("unsafe_request_wait %p wait on tid %llu %llu\n",
> inode, req1 ? req1->r_tid : 0ULL, req2 ? req2->r_tid : 0ULL);
> if (req1) {
> @@ -2321,6 +2398,7 @@ static int unsafe_request_wait(struct inode *inode)
> err = -EIO;
> ceph_mdsc_put_request(req2);
> }
> +out:
> return err;
> }
>
Otherwise the whole set looks pretty reasonable.
Thanks,
--
Jeff Layton <jlayton@xxxxxxxxxx>
