default or selected kernelversion does not have config value CONFIG_BLK_DEV_UMEM.
Result is shown for kernelversion 6.9.9

Micro Memory MM5415 Battery Backed RAM support

modulename: umem.ko

configname: CONFIG_BLK_DEV_UMEM

Linux Kernel Configuration
└─>Device Drivers
└─>Block devices
└─>Micro Memory MM5415 Battery Backed RAM support
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
Saying Y here will include support for the MM5415 family of
battery backed (Non-volatile) RAM cards.
<http://www.umem.com/>

The cards appear as block devices that can be partitioned into
as many as 15 partitions.

To compile this driver as a module, choose M here: the
module will be called umem.

The umem driver has not yet been allocated a MAJOR number, so
one is chosen dynamically.

source code: