As part of some protracted flailing around while trying to get GNU Radio running on a Raspberry Pi 3, I discovered Raspbian defaults to a 100 MB swap file, rather than a swap partition, and everything I thought I knew about swap management seems inoperative. The key hint came from some notes on gr-gsm installation.

Tweak the /etc/dphys-swapfile config file to set CONF_SWAPFACTOR=2 for a 2 GB swap file = twice the size of the Pi’s 1 GB memory.

Start it up:

sudo dphys-swapfile swapoff
sudo dphys-swapfile setup
sudo dphys-swapfile swapon

And verify it worked:

cat /proc/meminfo 
MemTotal:         949580 kB
MemFree:          194560 kB
MemAvailable:     594460 kB
Buffers:           85684 kB
Cached:           377276 kB
SwapCached:            0 kB
Active:           600332 kB
Inactive:         104668 kB
Active(anon):     250408 kB
Inactive(anon):    20688 kB
Active(file):     349924 kB
Inactive(file):    83980 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:       1918972 kB
SwapFree:        1918972 kB
Dirty:                40 kB
Writeback:             0 kB
AnonPages:        242072 kB
Mapped:           136072 kB
Shmem:             29060 kB
Slab:              33992 kB
SReclaimable:      22104 kB
SUnreclaim:        11888 kB
KernelStack:        1728 kB
PageTables:         3488 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     2393760 kB
Committed_AS:     947048 kB
VmallocTotal:    1114112 kB
VmallocUsed:           0 kB
VmallocChunk:          0 kB
CmaTotal:           8192 kB
CmaFree:            6796 kB

Then it became possible to continue flailing …