feat(memory): use fallocate(PUNCH_HOLE) for guest_memfd discard#5792
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JackThomson2 wants to merge 5 commits intofirecracker-microvm:feature/secret-hidingfrom
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feat(memory): use fallocate(PUNCH_HOLE) for guest_memfd discard#5792JackThomson2 wants to merge 5 commits intofirecracker-microvm:feature/secret-hidingfrom
JackThomson2 wants to merge 5 commits intofirecracker-microvm:feature/secret-hidingfrom
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Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## feature/secret-hiding #5792 +/- ##
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- Coverage 81.34% 81.31% -0.03%
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Files 279 279
Lines 30446 30451 +5
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- Hits 24766 24762 -4
- Misses 5680 5689 +9
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MADV_DONTNEED is a no-op for MAP_SHARED mappings, which means discard_range() previously did nothing for guest_memfd-backed memory. This prevented virtio-mem unplug and balloon inflate from actually freeing physical pages back to the host when secret_free is enabled. Add a fallocate(FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE) path for MAP_SHARED file-backed regions, which punches holes in the guest_memfd backing file and releases the pages from the page cache. Signed-off-by: Jack Thomson <jackabt@amazon.com>
Now that discard_range() uses fallocate(PUNCH_HOLE) for MAP_SHARED guest_memfd regions, the balloon can properly reclaim memory when secret_free is enabled. Remove the restriction that prevented combining balloon with secret_free. Signed-off-by: Jack Thomson <jackabt@amazon.com>
When secret_free is enabled, guest memory is backed by guest_memfd (MAP_SHARED). Host RSS doesn't reflect pages freed by fallocate(PUNCH_HOLE) — they're removed from the page cache, not RSS. Make get_stable_rss_mem() return guest-side memory usage (total - available) when uvm.secret_free is set. This is a closed system unaffected by host noise and correctly reflects balloon and virtio-mem operations. Signed-off-by: Jack Thomson <jackabt@amazon.com>
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Add the secret_free fixture parameter to all balloon functional tests, so they run with both SF_OFF and SF_ON variants. This exercises the fallocate(PUNCH_HOLE) discard path for guest_memfd-backed memory during balloon inflate/deflate. Signed-off-by: Jack Thomson <jackabt@amazon.com>
Now that discard_range() uses fallocate(PUNCH_HOLE) for guest_memfd, and get_resident_memory() uses guest meminfo for secret_free VMs, the RSS decrease assertion in check_hotunplug works correctly for secret_free. Remove the skip. Signed-off-by: Jack Thomson <jackabt@amazon.com>
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Add support for fallocate(PUNCH_HOLE) this will expand our tests to also include balloon and memory hotplugging tests
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CONTRIBUTING.md.PR Checklist
tools/devtool checkbuild --allto verify that the PR passesbuild checks on all supported architectures.
tools/devtool checkstyleto verify that the PR passes theautomated style checks.
how they are solving the problem in a clear and encompassing way.
in the PR.
CHANGELOG.md.Runbook for Firecracker API changes.
integration tests.
TODO.rust-vmm.MADV_DONTNEED is a no-op for MAP_SHARED mappings, which means
discard_range() previously did nothing for guest_memfd-backed memory.
This prevented virtio-mem unplug and balloon inflate from actually
freeing physical pages back to the host when secret_free is enabled.
Add a fallocate(FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE) path for
MAP_SHARED file-backed regions, which punches holes in the guest_memfd
backing file and releases the pages from the page cache.
Signed-off-by: Jack Thomson jackabt@amazon.com