fix(vmm): only use memfd if no vhost-user-blk devices configured #4498
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Codecov ReportAttention: Patch coverage is
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## main #4498 +/- ##
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- Coverage 81.63% 81.54% -0.10%
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Files 243 243
Lines 29825 29839 +14
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- Hits 24349 24333 -16
- Misses 5476 5506 +30
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Page faults are more expensive for shared memory mapping (like memfd). For this reason, we only back guest memory with a memfd if a vhost-user-blk device is configured in the VM, otherwise we fall back to anonymous private memory. This is recovering performance demonstrated before commit 027a992 had been merged. The vhost-user-blk branch in VM creation is not currently covered by Rust integration tests, because we are looking for a converging solution, so guest memory is always created in the same way, and implementing required integration test infrastructure code (spawing a backend process) would not be useful long term. Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
This is because guest memory is backed by anon private mapping in a regular case. Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
Huge pages tests search for memory mapping name, which is now anon private instead of memfd. Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
This brings the former negative file size limit test from before 60737eb , which is valid for anon private guest memory backing. Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
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Status: Awaiting review
roypat
previously approved these changes
Mar 14, 2024
bchalios
previously approved these changes
Mar 14, 2024
xmarcalx
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Mar 14, 2024
Mention memfd page fault overhead and host pagecache usage for virtio block devices compared to vhost-user. Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
Adds a changelog entry that VMs that do not use vhost-user-blk devices are backed by anon private memory mapping. Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
xmarcalx
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Mar 14, 2024
roypat
approved these changes
Mar 14, 2024
bchalios
approved these changes
Mar 15, 2024
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Changes
Only back guest memory with a memfd if a vhost-user-blk device is configured in the VM, otherwise fall back to anonymous private memory.
This is recovering performance demonstrated before commit 027a992 had been merged.
Reason
Page faults are more expensive for shared memory mapping (like memfd).
License Acceptance
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CONTRIBUTING.md.PR Checklist
[ ] If a specific issue led to this PR, this PR closes the issue.[ ] Any required documentation changes (code and docs) are included in thisPR.
[ ] API changes follow the Runbook for Firecracker API changes.CHANGELOG.md.[ ] NewTODOs link to an issue.contribution quality standards.
rust-vmm.