[1.6] fix(vmm): only use memfd if no vhost-user-blk devices configured #4502
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Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## firecracker-v1.6 #4502 +/- ##
====================================================
- Coverage 81.53% 81.47% -0.07%
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Files 240 240
Lines 29367 29377 +10
====================================================
- Hits 23945 23934 -11
- Misses 5422 5443 +21
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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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 <[email protected]>
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 <[email protected]>
This brings the former negative file size limit test from before 60737eb , which is valid for anon private guest memory backing. (cherry picked from commit 2c200e4) Signed-off-by: Nikita Kalyazin <[email protected]>
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 <[email protected]>
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 36e419166041b6ae61086045d2604d99457296c1) Signed-off-by: Nikita Kalyazin <[email protected]>
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|
we're going to suggest users to upgrade to 1.7 (released soon) if they are affected by memfd page fault latency. |
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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.