Merge pull request #42581 from CongMinYin/perf

librbd/cache/pwl: fix buf_persist and add writeback_lat perf counters

Reviewed-by: Ilya Dryomov <idryomov@gmail.com>

diff --cc src/librbd/cache/pwl/AbstractWriteLog.cc
Simple merge

diff --cc src/librbd/cache/pwl/LogOperation.cc
Simple merge

diff --cc src/librbd/cache/pwl/rwl/WriteLog.cc
Simple merge

diff --cc src/librbd/cache/pwl/ssd/WriteLog.cc
Simple merge