[v6,0/2] NFSD: delay unmount source's export after inter-server copy completed.

Message

Dai Ngo May 19, 2021, 8:44 p.m. UTC

Hi Olga, Bruce,

Currently the source's export is mounted and unmounted on every
inter-server copy operation. This causes unnecessary overhead
for each copy.

This patch series is an enhancement to allow the export to remain
mounted for a configurable period (default to 15 minutes). If the 
export is not being used for the configured time it will be unmounted
by a delayed task. If it's used again then its expiration time is
extended for another period.

Since mount and unmount are no longer done on every copy request,
the restriction of copy size (14*rsize), in __nfs4_copy_file_range,
is removed.

-Dai

v2: fix compiler warning of missing prototype.
v3: remove the used of semaphore.
    eliminated all RPC calls for subsequence mount by allowing
       all exports from one server to share one vfsmount.
    make inter-server threshold a module configuration parameter.
v4: convert nsui_refcnt to use refcount_t.
    add note about 20secs wait in nfsd4_interssc_connect.
    removed (14*rsize) restriction from __nfs4_copy_file_range.
v5: make use of the laundomat thread to service delayed unmount list.
    destroy delayed unmount list when nfsd is shutdown.
    make delayed unmount list per nfsd_net to support container.
v6: move content of nfsd4_ssc_umount in to nfsd_net.
    move code that manages the delayed unmount list
         from nfsd/nfs4proc.c to nfsd/nfs4state.c
    cleanup left over from previous versions.