Re: [PATCH v5 1/2] NFSD: delay unmount source's export after inter-server copy completed.

[dai.ngo@xxxxxxxxxx]

On 5/18/21 10:16 AM, Olga Kornievskaia wrote:
> Hi Dai,
>
> General review comments inline
>
> On Mon, May 17, 2021 at 6:43 PM Dai Ngo <dai.ngo@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >   fs/nfsd/netns.h         |   5 ++
> >   fs/nfsd/nfs4proc.c      | 216 +++++++++++++++++++++++++++++++++++++++++++++++-
> >   fs/nfsd/nfs4state.c     |   8 ++
> >   fs/nfsd/nfsd.h          |   6 ++
> >   fs/nfsd/nfssvc.c        |   3 +
> >   include/linux/nfs_ssc.h |  16 ++++
> >   6 files changed, 250 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> > index c330f5bd0cf3..6018e5050cb4 100644
> > --- a/fs/nfsd/netns.h
> > +++ b/fs/nfsd/netns.h
> > @@ -21,6 +21,7 @@
> >
> >   struct cld_net;
> >   struct nfsd4_client_tracking_ops;
> > +struct nfsd4_ssc_umount;
> >
> >   enum {
> >          /* cache misses due only to checksum comparison failures */
> > @@ -176,6 +177,10 @@ struct nfsd_net {
> >          unsigned int             longest_chain_cachesize;
> >
> >          struct shrinker         nfsd_reply_cache_shrinker;
> > +
> > +       spinlock_t              nfsd_ssc_lock;
> > +       struct nfsd4_ssc_umount *nfsd_ssc_umount;
> > +
> >          /* utsname taken from the process that starts the server */
> >          char                    nfsd_name[UNX_MAXNODENAME+1];
> >   };
> > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > index dd9f38d072dd..892ad72d87ae 100644
> > --- a/fs/nfsd/nfs4proc.c
> > +++ b/fs/nfsd/nfs4proc.c
> > @@ -55,6 +55,99 @@ 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");
> > +
> > +void nfsd4_ssc_expire_umount(struct nfsd_net *nn)
> Why should this be in nfs4proc.c when it's used in nfs4state.c only?

I will move nfsd4_ssc_expire_umount to nfs4state.c

> > +{
> > +       bool do_wakeup = false;
> > +       struct nfsd4_ssc_umount_item *ni = 0;
> > +       struct nfsd4_ssc_umount_item *tmp;
> > +       struct nfsd4_ssc_umount *nu;
> > +
> > +       spin_lock(&nn->nfsd_ssc_lock);
> > +       if (!nn->nfsd_ssc_umount) {
> > +               spin_unlock(&nn->nfsd_ssc_lock);
> > +               return;
> > +       }
> > +       nu = nn->nfsd_ssc_umount;
> > +       list_for_each_entry_safe(ni, tmp, &nu->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(&nn->nfsd_ssc_lock);
> > +                       mntput(ni->nsui_vfsmount);
> > +                       spin_lock(&nn->nfsd_ssc_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;
> mnt1, mnt2, mnt3  added all at the same time. mnt1, mnt3 only used
> once during the expiration time. mnt2 is being used continuously.

m2's nsu_expire is updated and re-inserted to the tail of the list
every time it's used.

> expiration time comes. delayed mnt1 is processed. mnt2 is next on the
> list and it's not expired so code quits. mnt3 will not be umounted
> until mnt2 expires. I think the break is wrong.

m1 and m3 will be processed first and unmounted if their nsu_expire
expires, m2 is last on the list.

-Dai

> > +       }
> > +       if (!list_empty(&nu->nsu_list)) {
> > +               ni = list_first_entry(&nu->nsu_list,
> > +                       struct nfsd4_ssc_umount_item, nsui_list);
> > +               nu->nsu_expire = ni->nsui_expire;
> > +       } else
> > +               nu->nsu_expire = 0;
> > +
> > +       if (do_wakeup)
> > +               wake_up_all(&nu->nsu_waitq);
> > +       spin_unlock(&nn->nfsd_ssc_lock);
> > +}
> > +
> > +/*
> > + * This is called when nfsd is being shutdown, after all inter_ssc
> > + * cleanup were done, to destroy the ssc delayed unmount list.
> > + */
> > +void nfsd4_ssc_shutdown_umount(struct nfsd_net *nn)
> > +{
> > +       struct nfsd4_ssc_umount_item *ni = 0;
> > +       struct nfsd4_ssc_umount_item *tmp;
> > +       struct nfsd4_ssc_umount *nu;
> > +
> > +       spin_lock(&nn->nfsd_ssc_lock);
> > +       if (!nn->nfsd_ssc_umount) {
> > +               spin_unlock(&nn->nfsd_ssc_lock);
> > +               return;
> > +       }
> > +       nu = nn->nfsd_ssc_umount;
> > +       nn->nfsd_ssc_umount = 0;
> > +       list_for_each_entry_safe(ni, tmp, &nu->nsu_list, nsui_list) {
> > +               list_del(&ni->nsui_list);
> > +               spin_unlock(&nn->nfsd_ssc_lock);
> > +               mntput(ni->nsui_vfsmount);
> > +               kfree(ni);
> > +               spin_lock(&nn->nfsd_ssc_lock);
> > +       }
> > +       spin_unlock(&nn->nfsd_ssc_lock);
> > +       kfree(nu);
> General question to maybe Bruce: can nfsd_net go away while a compound
> is using it ? I hope not.  I can't quite think thru the scenario where
> we started the async copy task but then somehow nfsd_net is going away
> before async_copy is done and if there is anything we need to take
> care of. I think the net shutdown would not find anything to free so
> it would just return. And the copy's cleanup would not find a nfsd_net
> and so it would right away unmount. This is more of thinking out loud
> but I'd like somebody else to confirm I'm correct that we are OK here.
>
> > +}
> > +
> > +void nfsd4_ssc_init_umount_work(struct nfsd_net *nn)
> > +{
> > +       nn->nfsd_ssc_umount = kzalloc(sizeof(struct nfsd4_ssc_umount),
> > +                                       GFP_KERNEL);
> > +       if (!nn->nfsd_ssc_umount)
> > +               return;
> > +       spin_lock_init(&nn->nfsd_ssc_lock);
> > +       INIT_LIST_HEAD(&nn->nfsd_ssc_umount->nsu_list);
> > +       init_waitqueue_head(&nn->nfsd_ssc_umount->nsu_waitq);
> > +}
> > +EXPORT_SYMBOL_GPL(nfsd4_ssc_init_umount_work);
> > +#endif
> > +
> >   #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
> >   #include <linux/security.h>
> >
> > @@ -1181,6 +1274,12 @@ 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 = NULL;
> > +       struct nfsd4_ssc_umount_item *tmp;
> > +       struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
> > +       struct nfsd4_ssc_umount *nu;
> > +       DEFINE_WAIT(wait);
> >
> >          naddr = &nss->u.nl4_addr;
> >          tmp_addrlen = rpc_uaddr2sockaddr(SVC_NET(rqstp), naddr->addr,
> > @@ -1229,12 +1328,76 @@ 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(&nn->nfsd_ssc_lock);
> > +       if (!nn->nfsd_ssc_umount) {
> > +               spin_unlock(&nn->nfsd_ssc_lock);
> > +               kfree(work);
> > +               work = NULL;
> > +               goto skip_dul;
> > +       }
> > +       nu = nn->nfsd_ssc_umount;
> > +       list_for_each_entry_safe(ni, tmp, &nu->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(&nu->nsu_waitq, &wait,
> > +                               TASK_INTERRUPTIBLE);
> > +                       spin_unlock(&nn->nfsd_ssc_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(&nu->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(&nn->nfsd_ssc_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, &nu->nsu_list);
> > +       }
> > +       spin_unlock(&nn->nfsd_ssc_lock);
> > +skip_dul:
> > +
> >          /* 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(&nn->nfsd_ssc_lock);
> > +                       list_del(&work->nsui_list);
> > +                       wake_up_all(&nu->nsu_waitq);
> > +                       spin_unlock(&nn->nfsd_ssc_lock);
> > +                       kfree(work);
> > +               }
> >                  goto out_free_devname;
> > -
> > +       }
> > +       if (work) {
> > +               spin_lock(&nn->nfsd_ssc_lock);
> > +               work->nsui_vfsmount = ss_mnt;
> > +               work->nsui_busy = false;
> > +               wake_up_all(&nu->nsu_waitq);
> > +               spin_unlock(&nn->nfsd_ssc_lock);
> > +       }
> > +out_done:
> >          status = 0;
> >          *mount = ss_mnt;
> >
> > @@ -1301,10 +1464,55 @@ 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;
> > +       struct nfsd4_ssc_umount *nu;
> > +       struct nfsd_net *nn = net_generic(dst->nf_net, nfsd_net_id);
> > +
> >          nfs42_ssc_close(src->nf_file);
> > -       fput(src->nf_file);
> >          nfsd_file_put(dst);
> > -       mntput(ss_mnt);
> > +       fput(src->nf_file);
> > +
> > +       if (!nn) {
> > +               mntput(ss_mnt);
> > +               return;
> > +       }
> > +       spin_lock(&nn->nfsd_ssc_lock);
> > +       if (!nn->nfsd_ssc_umount) {
> > +               /* delayed unmount list not setup */
> > +               spin_unlock(&nn->nfsd_ssc_lock);
> > +               mntput(ss_mnt);
> > +               return;
> > +       }
> > +       nu = nn->nfsd_ssc_umount;
> > +       timeout = msecs_to_jiffies(nfsd4_ssc_umount_timeout);
> > +       list_for_each_entry_safe(ni, tmp, &nu->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, &nu->nsu_list);
> > +                       found = true;
> > +                       break;
> > +               }
> > +       }
> > +       if (!found) {
> > +               spin_unlock(&nn->nfsd_ssc_lock);
> > +               mntput(ss_mnt);
> > +               return;
> > +       }
> > +       if (resched && !nu->nsu_expire)
> > +               nu->nsu_expire = ni->nsui_expire;
> > +       spin_unlock(&nn->nfsd_ssc_lock);
> >   }
> >
> >   #else /* CONFIG_NFSD_V4_2_INTER_SSC */
> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index 97447a64bad0..0cdc898f06c9 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -5459,6 +5459,11 @@ nfs4_laundromat(struct nfsd_net *nn)
> >                  list_del_init(&nbl->nbl_lru);
> >                  free_blocked_lock(nbl);
> >          }
> > +
> > +#ifdef CONFIG_NFSD_V4_2_INTER_SSC
> > +       /* service the inter-copy delayed unmount list */
> > +       nfsd4_ssc_expire_umount(nn);
> > +#endif
> >   out:
> >          new_timeo = max_t(time64_t, new_timeo, NFSD_LAUNDROMAT_MINTIMEOUT);
> >          return new_timeo;
> > @@ -7398,6 +7403,9 @@ nfs4_state_shutdown_net(struct net *net)
> >
> >          nfsd4_client_tracking_exit(net);
> >          nfs4_state_destroy_net(net);
> > +#ifdef CONFIG_NFSD_V4_2_INTER_SSC
> > +       nfsd4_ssc_shutdown_umount(nn);
> > +#endif
> >          mntput(nn->nfsd_mnt);
> >   }
> >
> > diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> > index 8bdc37aa2c2e..cf86d9010974 100644
> > --- a/fs/nfsd/nfsd.h
> > +++ b/fs/nfsd/nfsd.h
> > @@ -483,6 +483,12 @@ 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(struct nfsd_net *nn);
> > +extern void nfsd4_ssc_expire_umount(struct nfsd_net *nn);
> > +extern void nfsd4_ssc_shutdown_umount(struct nfsd_net *nn);
> > +#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..ce89a8fe07ff 100644
> > --- a/fs/nfsd/nfssvc.c
> > +++ b/fs/nfsd/nfssvc.c
> > @@ -403,6 +403,9 @@ static int nfsd_startup_net(int nrservs, struct net *net, const struct cred *cre
> >          if (ret)
> >                  goto out_filecache;
> >
> > +#ifdef CONFIG_NFSD_V4_2_INTER_SSC
> > +       nfsd4_ssc_init_umount_work(nn);
> > +#endif
> >          nn->nfsd_net_up = true;
> >          return 0;
> >
> > diff --git a/include/linux/nfs_ssc.h b/include/linux/nfs_ssc.h
> > index f5ba0fbff72f..18afe62988b5 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 +53,21 @@ 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;
> > +       unsigned long nsu_expire;
> > +       wait_queue_head_t nsu_waitq;
> > +};
> >   #endif
> >
> >   /*
> > --
> > 2.9.5