memtier - Man Page

memtier [ -r ratio ] [ -t thresholds ] program args...

memtier runs the given program, redirecting memory allocations to different memory tiers based on a given policy.  This allows unmodified programs to run following a non-greedy allocation scheme that avoids a performance cliff when DRAM is exhausted.

-r ratio

Specifies the ratio as a pair of integers separated by a colon, where the first number gives the relative share of near DRAM to be used while the second number gives "far" memory, be it CXL memory or PMEM.  Eg. "1:4" means that 20% of allocations will use DRAM, 80% PMEM.

If the ratio is not given, it defaults to the relative share of physically installed memory.

This version of memtier recognizes only two tiers (DRAM and KMEM_DAX).

-t thresholds

Turns on DYNAMIC_THRESHOLD mode where small allocations are served from DRAM and large ones from far memory.  The syntax is described in depth in man libmemtier, eg. -t INIT_VAL=1024,MIN_VAL=512,MAX_VAL=65536 starts with a threshold of 1024, then varies it between 512..65536 attempting to match the requested ratio.

-v

Displays settings that are passed to libmemtier.

-h

Shows a help message then exits.

This tool doesn't expose all features of libmemtier.  Only DRAM and KMEM_DAX memory is supported, to use FS_DAX you need to configure the library directly, please refer to its man page.

Or alternatively, you can switch that memory to KMEM_DAX mode.  For that purpose, please refer to "man ndctl-reconfigure-namespace" and "man daxctl-reconfigure-device".

libmemtier(7), memkind(3), malloc(3)