Merge PR #22970 into master

* refs/pull/22970/head:
	os/bluestore: limit OSD memory usage by tuning the cache size.

Reviewed-by: Sage Weil <sage@redhat.com>

diff --cc src/common/options.cc
Simple merge

diff --cc src/os/CMakeLists.txt
Simple merge

diff --cc src/os/bluestore/BlueStore.cc
Simple merge