bigint-syrk-blas: account for MPI shared memory limits

[vasdommes]

Subtasks:

• bigint-syrk-blas: add --maxSharedMemory option to limit MPI shared memory window sizes #203
• bigint-syrk-blas: split P window according to --maxSharedMemory limit #204
• bigint-syrk-blas: split Q window, if it does not fit into the --maxSharedMemory limit #205
• Determine --maxSharedMemory automatically #206

See details in https://github.com/davidsd/sdpb/blob/bigint-syrk-blas/src/sdp_solve/SDP_Solver/run/bigint_syrk/Readme.md

For large problems, shared memory windows for P and/or Q do not fit into memory. Note also that sometimes HPC administrators may set limit for shared window size e.g. to 50% of available RAM, so that exceeding this limit may result in a warning and (most probably) crash:

It appears as if there is not enough space for
/tmp/openmpi-sessions-***@n131702_0/23041/1/0/shared_window_4.n131702
(the shared-memory backing file).
It is likely that your MPI job will now either abort or experience performance degradation.

Local host: n131702
Space Requested: 6710890760 B
Space Available: 6433673216 B

We can introduce new command-line argument for SDPB, e.g. --maxSharedMemory=128G #203

If total size for P and Q windows exceeds maxSharedMemory, we should split them and process part by part, #204 #205

We can also limit shared window size automatically, using our memory estimates for blocks together with MemAvailable from /proc/meminfo #206