Rob Bradford ffeee2880f vmm: memory_manager: Handle sparse snapshot file on restore ...

Walk the input snapshot file extent by extent via lseek(SEEK_DATA) /
lseek(SEEK_HOLE) within each region's slot and read only those bytes
into guest RAM via the existing read_volatile_from primitive. Holes are
left as the guest mapping's natural zero-fill, which matches the source
content.

Symmetric counterpart to sparse-write on snapshot. Works for both new
sparse snapshots and old dense snapshots: a dense file has no holes, so
SEEK_DATA returns the full range as one extent and the I/O pattern
matches the previous behaviour.

If the input file's filesystem does not support SEEK_HOLE the code falls
back to the existing dense read path.

Measured on a 4 GiB shared-memory VM (2 vCPUs, ~340 MiB touched), total
restore time as reported by the in-tree timing instrumentation:

  Before (dense):  ~1487ms, reads 4.0 GiB from file
  After (sparse):  ~136ms,  reads 340 MiB from file (92% less I/O, 11x faster)

Assisted-by: Claude:Opus-4.7
Signed-off-by: Rob Bradford <rbradford@meta.com>

2026-05-01 15:40:50 +00:00

..

src

vmm: memory_manager: Handle sparse snapshot file on restore

2026-05-01 15:40:50 +00:00

build.rs

build: Add "fuzzing" as a valid cfg(..) attribute

2024-05-08 08:10:28 +00:00

Cargo.toml

vmm: memory_manager: Add SEEK_DATA-based extent iterator

2026-05-01 15:40:50 +00:00