The synchronize_rcu() call can be eliminated to improve memory deregistration
performance.
There are two key fields involved:
- The rcu pointer itself
- the lkey_published field
To close the window between the rcu read of the mregion pointer and the
reference count the code should:
1. To lkey/rkey validation (reader)
Read the rcu pointer. If the pointer is non-NULL, get a reference.
To the current validation tests use a READ_ONCE() on the lkey_published.
Upon any failure release the reference.
2. To the remove logic (delete)
Insure the published is zeroed prior to setting the pointer to NULL.
This requires using rcu_assign_pointer() to insure lkey_published
is written prior to the NULL.
3. To the insert logic (add)
Insure the published is set use an rcu_assign_pointer() to insure the
pointer is after all MR fields.
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
b58fc80497