А между тем, ISPManager потребляет порядка 35 мегабайт памяти...

cat /proc/18281/status
Name: ispmgr
State: S (sleeping)
SleepAVG: 78%
Tgid: 18281
Pid: 18281
PPid: 1
TracerPid: 0
FNid: 6041
Uid: 0 0 0 0
Gid: 0 0 0 0
FDSize: 256
Groups: 33
envID: 6041
VPid: 18281
PNState: 0
StopState: 0
VmPeak: 35368 kB
VmSize: 35364 kB
VmLck: 0 kB
VmHWM: 8936 kB
VmRSS: 8788 kB
VmData: 23984 kB
VmStk: 84 kB
VmExe: 860 kB
VmLib: 9824 kB
VmPTE: 64 kB
StaBrk: 08d85000 kB
Brk: 090a0000 kB
StaStk: bff4e490 kB
Threads: 1
SigQ: 0/38912
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000001000
SigCgt: 0000000180006000
SigSvd: 0000000000000000
CapInh: 000000007dcceeff
CapPrm: 000000007dcceeff
CapEff: 000000007dcceeff
Cpus_allowed: ffffffff
Mems_allowed: 1
TaskUB: 6041
MMUB: 6041

VmSize как раз и есть ключевое значение, указываемое в top.