Zach Brown f52dc28322 scoutfs: simplify lock use of kernel dlm ...

We had an excessive number of layers between scoutfs and the dlm code in
the kernel.  We had dlmglue, the scoutfs locks, and task refs.  Each
layer had structs that track the lifetime of the layer below it.  We
were about to add another layer to hold on to locks just a bit longer so
that we can avoid down conversion and transaction commit storms under
contention.

This collapses all those layers into simple state machine in lock.c that
manages the mode of dlm locks on behalf of the file system.

The users of the lock interface are mainly unchanged.  We did change
from a heavier trylock to a lighter nonblock lock attempt and have to
change the single rare readpage use.  Lock fields change so a few
external users of those fields change.

This not only removes a lot of code it also contains functional
improvements.  For example, it can now convert directly to CW locks with
a single lock request instead of having to use two by first converting
to NL.

It introduces the concept of an unlock grace period.  Locks won't be
dropped on behalf of other nodes soon after being unlocked so that tasks
have a chance to batch up work before the other node gets a chance.
This can result in two orders of magnitude improvements in the time it
takes to, say, change a set of xattrs on the same file population from
two nodes concurrently.

There are significant changes to trace points, counters, and debug files
that follow the implementation changes.

Signed-off-by: Zach Brown <zab@versity.com>

2018-02-14 15:00:17 -08:00

kmod

scoutfs: simplify lock use of kernel dlm

2018-02-14 15:00:17 -08:00

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