[1.7] fix(vmm): only use memfd if no vhost-user-blk devices configured #4501
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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. (cherry picked from commit 931207b) Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
This is because guest memory is backed by anon private mapping in a regular case. (cherry picked from commit d6a775d) Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
Huge pages tests search for memory mapping name, which is now anon private instead of memfd. (cherry picked from commit eb219d7) Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
Mention memfd page fault overhead and host pagecache usage for virtio block devices compared to vhost-user. (cherry picked from commit 8ed3e4a) 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. (cherry picked from commit a6ee3b5) Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
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roypat
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bchalios
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Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## firecracker-v1.7 #4501 +/- ##
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- Coverage 81.65% 81.55% -0.10%
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Files 243 243
Lines 29834 29848 +14
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- Hits 24360 24344 -16
- Misses 5474 5504 +30
Flags with carried forward coverage won't be shown. Click here to find out more. ☔ View full report in Codecov by Sentry. |
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Changes
Backport #4498
Reason
To avoid page fault latency regression.
License Acceptance
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CONTRIBUTING.md.PR Checklist
[ ] If a specific issue led to this PR, this PR closes the issue.[ ] The description of changes is clear and encompassing.[ ] Any required documentation changes (code and docs) are included in thisPR.
[ ] API changes follow the Runbook for Firecracker API changes.CHANGELOG.md.[ ] All added/changed functionality is tested.[ ] NewTODOs link to an issue.contribution quality standards.
rust-vmm.