[$] Mitigating vmap lock contention

The "vmap area" is a range of kernel address space used when the kernelneeds to virtually map a range of memory; among other things, memoryallocations obtained from vmalloc() and loadable modules areplaced there. At the 2023 Linux Storage,Filesystem, Memory-Management and BPF Summit, Uladzislau Rezki,presenting remotely, explained a performance problem related to the vmap area and discussedpossible solutions.