The current VMA cache implementation backing rcache/grdma can run into
a deadlock situation in multi-threaded code when madvise is hooked and
the c library uses locks. In this case we may run into the following
situation:
Thread 1:
...
free () <- Holding libc lock
madvice_hook ()
vma_iteration () <- Blocked waiting for vma lock
Thread 2:
...
vma_insert () <- Holding vma lock
vma_item_new ()
malloc () <- Blocked waiting for libc lock
To fix this problem we chose to remove the madvise () hook but that
fix is causing issue #3685. This commit aims to greatly reduce the
chance that the deadlock will be hit by putting vma items into a free
list. This moves the allocation outside the vma lock. In general there
are a relatively small number of vma items so the default is to
allocate 2048 vma items. This default is configurable but it is likely
the number is too large not too small.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
b6bf3f4d95