tcmalloc: ability to disable fallback allocator in memfs

Whenever tcmalloc memfs allocator runs out of huge memory, it falls back to the
default system allocator, which will start allocating from normal anonymous
memory pool (small pages).  For use cases that exclusively want hugepage backed
memory, such as using tcmalloc in combination with Intel SPDK, this is

This change adds an environment variable "TCMALLOC_MEMFS_DISABLE_FALLBACK"
which when set to true will ensure that tcmalloc doesn't fallback to using the
system allocator when the system runs out of hugepages. This is false by
default, such that all other tcmalloc consumers will not see any changes.

For those curious, you can see part of our upstream SPDK work here:
1 file changed