I checked a 512M guest which has with some overhead ~550M
The majority is the unique guest memory and qemu allocations.
And a slight bit out of shared mappings.
PID User Command Swap USS PSS RSS
65719 libvirt-qemu /usr/bin/qemu-system-x86_64 4.0K 549.5M 550.6M
554.3M
ps_mem here reports 1.1G which is wrong
Private + Shared = RAM used Program
549.3 MiB + 551.6 MiB = 1.1 GiB qemu-system-x86_64
If you look in /proc/<pid>smaps you'll find that qemu has
the usual libs and a few unpopulated 64M mappings.
The real majority of memory consumption is in the mapping
of the guest memory.
7fb9b3e00000-7fb9d3e00000 rw-p 00000000 00:00 0
Size: 524288 kB
KernelPageSize: 4 kB
MMUPageSize: 4 kB
Rss: 524176 kB
Pss: 524176 kB
Shared_Clean: 0 kB
Shared_Dirty: 0 kB
Private_Clean: 0 kB
Private_Dirty: 524176 kB
Referenced: 519084 kB
Anonymous: 524176 kB
LazyFree: 0 kB
AnonHugePages: 0 kB
ShmemPmdMapped: 0 kB
FilePmdMapped: 0 kB
Shared_Hugetlb: 0 kB
Private_Hugetlb: 0 kB
Swap: 0 kB
SwapPss: 0 kB
Locked: 0 kB
THPeligible: 1
VmFlags: rd wr mr mw me dc ac dd sd hg mg
There just isn't much more than that:
root@g-newqemu:~# cat /proc/65719/smaps | grep -e '^Rss' | awk 'BEGIN {sum=0}
{sum=sum+$2} END {print sum}'
567464
root@g-newqemu:~# cat /proc/65719/smaps | grep -e '^Pss' | awk 'BEGIN {sum=0}
{sum=sum+$2} END {print sum}'
563837
ps_mem just has a bug in this case,
one can have a shared mapping without shared bytes.
But ps_mem does parse shared and pss to then recalculate it as:
Shared = Pss - Private
That is just wrong, shared is zero.
The calculation above makes it assume twice as much memory as is really
consumed.
As ps_mem isn't in Ubuntu that is at best a bug report at
https://github.com/pixelb/ps_mem/issues
** Changed in: qemu (Ubuntu)
Status: Incomplete => Invalid
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https://bugs.launchpad.net/bugs/1892648
Title:
VM eating twice the memory allocated
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