Re: [PATCH v4 1/2] NFSD: delay unmount source's export after inter-server copy completed.

["J. Bruce Fields" <bfields@fieldses.org>]

On Fri, May 14, 2021 at 02:12:38PM -0400, Olga Kornievskaia wrote:
> On Fri, Apr 23, 2021 at 4:59 PM Dai Ngo <dai.ngo@oracle.com> wrote:
> >
> > Currently the source's export is mounted and unmounted on every
> > inter-server copy operation. This patch is an enhancement to delay
> > the unmount of the source export for a certain period of time to
> > eliminate the mount and unmount overhead on subsequent copy operations.
> >
> > After a copy operation completes, a delayed task is scheduled to
> > unmount the export after a configurable idle time. Each time the
> > export is being used again, its expire time is extended to allow
> > the export to remain mounted.
> >
> > The unmount task and the mount operation of the copy request are
> > synced to make sure the export is not unmounted while it's being
> > used.
> >
> > Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> > ---
> >  fs/nfsd/nfs4proc.c      | 178 ++++++++++++++++++++++++++++++++++++++++++++++--
> >  fs/nfsd/nfsd.h          |   4 ++
> >  fs/nfsd/nfssvc.c        |   3 +
> >  include/linux/nfs_ssc.h |  20 ++++++
> >  4 files changed, 201 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > index dd9f38d072dd..a4b110cbcab5 100644
> > --- a/fs/nfsd/nfs4proc.c
> > +++ b/fs/nfsd/nfs4proc.c
> > @@ -55,6 +55,81 @@ module_param(inter_copy_offload_enable, bool, 0644);
> >  MODULE_PARM_DESC(inter_copy_offload_enable,
> >                  "Enable inter server to server copy offload. Default: false");
> >
> > +#ifdef CONFIG_NFSD_V4_2_INTER_SSC
> > +static int nfsd4_ssc_umount_timeout = 900000;          /* default to 15 mins */
> > +module_param(nfsd4_ssc_umount_timeout, int, 0644);
> > +MODULE_PARM_DESC(nfsd4_ssc_umount_timeout,
> > +               "idle msecs before unmount export from source server");
> > +
> > +static void nfsd4_ssc_expire_umount(struct work_struct *work);
> > +static struct nfsd4_ssc_umount nfsd4_ssc_umount;
> > +
> > +/* nfsd4_ssc_umount.nsu_lock must be held */
> > +static void nfsd4_scc_update_umnt_timo(void)
> > +{
> > +       struct nfsd4_ssc_umount_item *ni = 0;
> > +
> > +       cancel_delayed_work(&nfsd4_ssc_umount.nsu_umount_work);
> > +       if (!list_empty(&nfsd4_ssc_umount.nsu_list)) {
> > +               ni = list_first_entry(&nfsd4_ssc_umount.nsu_list,
> > +                       struct nfsd4_ssc_umount_item, nsui_list);
> > +               nfsd4_ssc_umount.nsu_expire = ni->nsui_expire;
> > +               schedule_delayed_work(&nfsd4_ssc_umount.nsu_umount_work,
> > +                       ni->nsui_expire - jiffies);
> > +       } else
> > +               nfsd4_ssc_umount.nsu_expire = 0;
> > +}
> > +
> > +static void nfsd4_ssc_expire_umount(struct work_struct *work)
> > +{
> > +       bool do_wakeup = false;
> > +       struct nfsd4_ssc_umount_item *ni = 0;
> > +       struct nfsd4_ssc_umount_item *tmp;
> > +
> > +       spin_lock(&nfsd4_ssc_umount.nsu_lock);
> > +       list_for_each_entry_safe(ni, tmp, &nfsd4_ssc_umount.nsu_list, nsui_list) {
> > +               if (time_after(jiffies, ni->nsui_expire)) {
> > +                       if (refcount_read(&ni->nsui_refcnt) > 0)
> > +                               continue;
> > +
> > +                       /* mark being unmount */
> > +                       ni->nsui_busy = true;
> > +                       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
> > +                       mntput(ni->nsui_vfsmount);
> > +                       spin_lock(&nfsd4_ssc_umount.nsu_lock);
> > +
> > +                       /* waiters need to start from begin of list */
> > +                       list_del(&ni->nsui_list);
> > +                       kfree(ni);
> > +
> > +                       /* wakeup ssc_connect waiters */
> > +                       do_wakeup = true;
> > +                       continue;
> > +               }
> > +               break;
> 
> Wouldn't you be exiting your iteration loop as soon as you find a
> delayed item that hasn't expired? What if other items on the list have
> expired?
> 
> It looks like the general design is that work for doing umount is
> triggered by doing some copy, right? And then it just keeps
> rescheduling itself? Shouldn't we just be using the laundrymat instead
> that wakes up and goes thru the list mounts that are put to be
> unmounted and does so? Bruce previously had suggested using laundrymat
> for cleaning up copynotify states on the source server. But if the
> existing approach works for Bruce, I'm ok with it too.

I guess I'd prefer to use the laundromat, unless there's some reason to
do this one differently.

Also: on a quick skim, I don't see where this is shut down?  (If the
server is shut down, or the module unloaded?)

--b.

> 
> > +       }
> > +       nfsd4_scc_update_umnt_timo();
> > +       if (do_wakeup)
> > +               wake_up_all(&nfsd4_ssc_umount.nsu_waitq);
> > +       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
> > +}
> > +
> > +static DECLARE_DELAYED_WORK(nfsd4, nfsd4_ssc_expire_umount);
> > +
> > +void nfsd4_ssc_init_umount_work(void)
> > +{
> > +       if (nfsd4_ssc_umount.nsu_inited)
> > +               return;
> > +       INIT_DELAYED_WORK(&nfsd4_ssc_umount.nsu_umount_work,
> > +               nfsd4_ssc_expire_umount);
> > +       INIT_LIST_HEAD(&nfsd4_ssc_umount.nsu_list);
> > +       spin_lock_init(&nfsd4_ssc_umount.nsu_lock);
> > +       init_waitqueue_head(&nfsd4_ssc_umount.nsu_waitq);
> > +       nfsd4_ssc_umount.nsu_inited = true;
> > +}
> > +EXPORT_SYMBOL_GPL(nfsd4_ssc_init_umount_work);
> > +#endif
> > +
> >  #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
> >  #include <linux/security.h>
> >
> > @@ -1181,6 +1256,9 @@ nfsd4_interssc_connect(struct nl4_server *nss, struct svc_rqst *rqstp,
> >         char *ipaddr, *dev_name, *raw_data;
> >         int len, raw_len;
> >         __be32 status = nfserr_inval;
> > +       struct nfsd4_ssc_umount_item *ni = 0;
> > +       struct nfsd4_ssc_umount_item *work, *tmp;
> > +       DEFINE_WAIT(wait);
> >
> >         naddr = &nss->u.nl4_addr;
> >         tmp_addrlen = rpc_uaddr2sockaddr(SVC_NET(rqstp), naddr->addr,
> > @@ -1229,12 +1307,68 @@ nfsd4_interssc_connect(struct nl4_server *nss, struct svc_rqst *rqstp,
> >                 goto out_free_rawdata;
> >         snprintf(dev_name, len + 5, "%s%s%s:/", startsep, ipaddr, endsep);
> >
> > +       work = kzalloc(sizeof(*work), GFP_KERNEL);
> > +try_again:
> > +       spin_lock(&nfsd4_ssc_umount.nsu_lock);
> > +       list_for_each_entry_safe(ni, tmp, &nfsd4_ssc_umount.nsu_list, nsui_list) {
> > +               if (strncmp(ni->nsui_ipaddr, ipaddr, sizeof(ni->nsui_ipaddr)))
> > +                       continue;
> > +               /* found a match */
> > +               if (ni->nsui_busy) {
> > +                       /*  wait - and try again */
> > +                       prepare_to_wait(&nfsd4_ssc_umount.nsu_waitq, &wait,
> > +                               TASK_INTERRUPTIBLE);
> > +                       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
> > +
> > +                       /* allow 20secs for mount/unmount for now - revisit */
> > +                       if (signal_pending(current) ||
> > +                                       (schedule_timeout(20*HZ) == 0)) {
> > +                               status = nfserr_eagain;
> > +                               kfree(work);
> > +                               goto out_free_devname;
> > +                       }
> > +                       finish_wait(&nfsd4_ssc_umount.nsu_waitq, &wait);
> > +                       goto try_again;
> > +               }
> > +               ss_mnt = ni->nsui_vfsmount;
> > +               if (refcount_read(&ni->nsui_refcnt) == 0)
> > +                       refcount_set(&ni->nsui_refcnt, 1);
> > +               else
> > +                       refcount_inc(&ni->nsui_refcnt);
> > +               spin_unlock(&nfsd4_ssc_umount.nsu_lock);
> > +               kfree(work);
> > +               goto out_done;
> > +       }
> > +       /* create new entry, set busy, insert list, clear busy after mount */
> > +       if (work) {
> > +               strncpy(work->nsui_ipaddr, ipaddr, sizeof(work->nsui_ipaddr));
> > +               refcount_set(&work->nsui_refcnt, 1);
> > +               work->nsui_busy = true;
> > +               list_add_tail(&work->nsui_list, &nfsd4_ssc_umount.nsu_list);
> > +       }
> > +       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
> > +
> >         /* Use an 'internal' mount: SB_KERNMOUNT -> MNT_INTERNAL */
> >         ss_mnt = vfs_kern_mount(type, SB_KERNMOUNT, dev_name, raw_data);
> >         module_put(type->owner);
> > -       if (IS_ERR(ss_mnt))
> > +       if (IS_ERR(ss_mnt)) {
> > +               if (work) {
> > +                       spin_lock(&nfsd4_ssc_umount.nsu_lock);
> > +                       list_del(&work->nsui_list);
> > +                       wake_up_all(&nfsd4_ssc_umount.nsu_waitq);
> > +                       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
> > +                       kfree(work);
> > +               }
> >                 goto out_free_devname;
> > -
> > +       }
> > +       if (work) {
> > +               spin_lock(&nfsd4_ssc_umount.nsu_lock);
> > +               work->nsui_vfsmount = ss_mnt;
> > +               work->nsui_busy = false;
> > +               wake_up_all(&nfsd4_ssc_umount.nsu_waitq);
> > +               spin_unlock(&nfsd4_ssc_umount.nsu_lock);
> > +       }
> > +out_done:
> >         status = 0;
> >         *mount = ss_mnt;
> >
> > @@ -1301,10 +1435,46 @@ static void
> >  nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct nfsd_file *src,
> >                         struct nfsd_file *dst)
> >  {
> > +       bool found = false;
> > +       bool resched = false;
> > +       long timeout;
> > +       struct nfsd4_ssc_umount_item *tmp;
> > +       struct nfsd4_ssc_umount_item *ni = 0;
> > +
> >         nfs42_ssc_close(src->nf_file);
> > -       fput(src->nf_file);
> >         nfsd_file_put(dst);
> > -       mntput(ss_mnt);
> > +       fput(src->nf_file);
> > +
> > +       timeout = msecs_to_jiffies(nfsd4_ssc_umount_timeout);
> > +       spin_lock(&nfsd4_ssc_umount.nsu_lock);
> > +       list_for_each_entry_safe(ni, tmp, &nfsd4_ssc_umount.nsu_list,
> > +               nsui_list) {
> > +               if (ni->nsui_vfsmount->mnt_sb == ss_mnt->mnt_sb) {
> > +                       list_del(&ni->nsui_list);
> > +                       /*
> > +                        * vfsmount can be shared by multiple exports,
> > +                        * decrement refcnt and schedule delayed task
> > +                        * if it drops to 0.
> > +                        */
> > +                       if (refcount_dec_and_test(&ni->nsui_refcnt))
> > +                               resched = true;
> > +                       ni->nsui_expire = jiffies + timeout;
> > +                       list_add_tail(&ni->nsui_list, &nfsd4_ssc_umount.nsu_list);
> > +                       found = true;
> > +                       break;
> > +               }
> > +       }
> > +       if (!found) {
> > +               spin_unlock(&nfsd4_ssc_umount.nsu_lock);
> > +               mntput(ss_mnt);
> > +               return;
> > +       }
> > +       if (resched && !nfsd4_ssc_umount.nsu_expire) {
> > +               nfsd4_ssc_umount.nsu_expire = ni->nsui_expire;
> > +               schedule_delayed_work(&nfsd4_ssc_umount.nsu_umount_work,
> > +                               timeout);
> > +       }
> > +       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
> >  }
> >
> >  #else /* CONFIG_NFSD_V4_2_INTER_SSC */
> > diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> > index 8bdc37aa2c2e..b3bf8a5f4472 100644
> > --- a/fs/nfsd/nfsd.h
> > +++ b/fs/nfsd/nfsd.h
> > @@ -483,6 +483,10 @@ static inline bool nfsd_attrs_supported(u32 minorversion, const u32 *bmval)
> >  extern int nfsd4_is_junction(struct dentry *dentry);
> >  extern int register_cld_notifier(void);
> >  extern void unregister_cld_notifier(void);
> > +#ifdef CONFIG_NFSD_V4_2_INTER_SSC
> > +extern void nfsd4_ssc_init_umount_work(void);
> > +#endif
> > +
> >  #else /* CONFIG_NFSD_V4 */
> >  static inline int nfsd4_is_junction(struct dentry *dentry)
> >  {
> > diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> > index 6de406322106..2558db55b88b 100644
> > --- a/fs/nfsd/nfssvc.c
> > +++ b/fs/nfsd/nfssvc.c
> > @@ -322,6 +322,9 @@ static int nfsd_startup_generic(int nrservs)
> >         ret = nfs4_state_start();
> >         if (ret)
> >                 goto out_file_cache;
> > +#ifdef CONFIG_NFSD_V4_2_INTER_SSC
> > +       nfsd4_ssc_init_umount_work();
> > +#endif
> >         return 0;
> >
> >  out_file_cache:
> > diff --git a/include/linux/nfs_ssc.h b/include/linux/nfs_ssc.h
> > index f5ba0fbff72f..1e07be2a89fa 100644
> > --- a/include/linux/nfs_ssc.h
> > +++ b/include/linux/nfs_ssc.h
> > @@ -8,6 +8,7 @@
> >   */
> >
> >  #include <linux/nfs_fs.h>
> > +#include <linux/sunrpc/svc.h>
> >
> >  extern struct nfs_ssc_client_ops_tbl nfs_ssc_client_tbl;
> >
> > @@ -52,6 +53,25 @@ static inline void nfs42_ssc_close(struct file *filep)
> >         if (nfs_ssc_client_tbl.ssc_nfs4_ops)
> >                 (*nfs_ssc_client_tbl.ssc_nfs4_ops->sco_close)(filep);
> >  }
> > +
> > +struct nfsd4_ssc_umount_item {
> > +       struct list_head nsui_list;
> > +       bool nsui_busy;
> > +       refcount_t nsui_refcnt;
> > +       unsigned long nsui_expire;
> > +       struct vfsmount *nsui_vfsmount;
> > +       char nsui_ipaddr[RPC_MAX_ADDRBUFLEN];
> > +};
> > +
> > +struct nfsd4_ssc_umount {
> > +       struct list_head nsu_list;
> > +       struct delayed_work nsu_umount_work;
> > +       spinlock_t nsu_lock;
> > +       unsigned long nsu_expire;
> > +       wait_queue_head_t nsu_waitq;
> > +       bool nsu_inited;
> > +};
> > +
> >  #endif
> >
> >  /*
> > --
> > 2.9.5
> >