runsc: do not account memory of disk backed private MemoryFiles - #16619

A private MemoryFile backs a disk backed overlay or tmpfs mount with a host
file. While the sandbox runs, pages written to it are never reported as memory
usage: they are allocated without being marked committed, and only the main
MemoryFile is scanned for committed pages. MemoryFile.SaveTo marks every page
with data as committed and LoadFrom accounts every restored page, though, so a
checkpoint turns the whole file into Tmpfs usage for the running sandbox, and
a restored sandbox reports it for its lifetime. A sandbox that copied 15 GB of
database files into its rootfs overlay reported 18 GB of memory after restore
while holding 3 GB.

The pages of a disk backed file are host page cache for that file, which the
host can drop at any time, so they are not memory held by the sandbox.
Disable memory accounting for private MemoryFiles so that neither the running
nor the restored sandbox reports them.

FUTURE_COPYBARA_INTEGRATE_REVIEW=#16619 from ayushr2:private-mf-no-accounting 0af51ca
PiperOrigin-RevId: 1009219970

A private MemoryFile backs a disk backed overlay or tmpfs mount with a host
file. While the sandbox runs, pages written to it are never reported as memory
usage: they are allocated without being marked committed, and only the main
MemoryFile is scanned for committed pages. MemoryFile.SaveTo marks every page
with data as committed and LoadFrom accounts every restored page, though, so a
checkpoint turns the whole file into Tmpfs usage for the running sandbox, and
a restored sandbox reports it for its lifetime. A sandbox that copied 15 GB of
database files into its rootfs overlay reported 18 GB of memory after restore
while holding 3 GB.

The pages of a disk backed file are host page cache for that file, which the
host can drop at any time, so they are not memory held by the sandbox.
Disable memory accounting for private MemoryFiles so that neither the running
nor the restored sandbox reports them.

FUTURE_COPYBARA_INTEGRATE_REVIEW=#16619 from ayushr2:private-mf-no-accounting 0af51ca
PiperOrigin-RevId: 1009219970

A private MemoryFile backs a disk backed overlay or tmpfs mount with a host
file. While the sandbox runs, pages written to it are never reported as memory
usage: they are allocated without being marked committed, and only the main
MemoryFile is scanned for committed pages. MemoryFile.SaveTo marks every page
with data as committed and LoadFrom accounts every restored page, though, so a
checkpoint turns the whole file into Tmpfs usage for the running sandbox, and
a restored sandbox reports it for its lifetime. A sandbox that copied 15 GB of
database files into its rootfs overlay reported 18 GB of memory after restore
while holding 3 GB.

The pages of a disk backed file are host page cache for that file, which the
host can drop at any time, so they are not memory held by the sandbox.
Disable memory accounting for private MemoryFiles so that neither the running
nor the restored sandbox reports them.

FUTURE_COPYBARA_INTEGRATE_REVIEW=#16619 from ayushr2:private-mf-no-accounting 0af51ca
PiperOrigin-RevId: 1009219970

A private MemoryFile backs a disk backed overlay or tmpfs mount with a host
file. While the sandbox runs, pages written to it are never reported as memory
usage: they are allocated without being marked committed, and only the main
MemoryFile is scanned for committed pages. MemoryFile.SaveTo marks every page
with data as committed and LoadFrom accounts every restored page, though, so a
checkpoint turns the whole file into Tmpfs usage for the running sandbox, and
a restored sandbox reports it for its lifetime. A sandbox that copied 15 GB of
database files into its rootfs overlay reported 18 GB of memory after restore
while holding 3 GB.

The pages of a disk backed file are host page cache for that file, which the
host can drop at any time, so they are not memory held by the sandbox.
Disable memory accounting for private MemoryFiles so that neither the running
nor the restored sandbox reports them.

FUTURE_COPYBARA_INTEGRATE_REVIEW=#16619 from ayushr2:private-mf-no-accounting 0af51ca
PiperOrigin-RevId: 1009219970

A private MemoryFile backs a disk backed overlay or tmpfs mount with a host
file. While the sandbox runs, pages written to it are never reported as memory
usage: they are allocated without being marked committed, and only the main
MemoryFile is scanned for committed pages. MemoryFile.SaveTo marks every page
with data as committed and LoadFrom accounts every restored page, though, so a
checkpoint turns the whole file into Tmpfs usage for the running sandbox, and
a restored sandbox reports it for its lifetime. A sandbox that copied 15 GB of
database files into its rootfs overlay reported 18 GB of memory after restore
while holding 3 GB.

The pages of a disk backed file are host page cache for that file, which the
host can drop at any time, so they are not memory held by the sandbox.
Disable memory accounting for private MemoryFiles so that neither the running
nor the restored sandbox reports them.
Auto-fixed-by: [🤖] @EtiennePerot
FUTURE_COPYBARA_INTEGRATE_REVIEW=#16619 from ayushr2:private-mf-no-accounting 0af51ca
PiperOrigin-RevId: 1010803299