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…ght-dev#1788)" This reverts commit 3ef1a36. On Windows, a snapshot blob marked with FSCTL_SET_SPARSE is slow to map under WHP. The first guest function call after restoring from it takes about 35 ms longer than from a dense blob. Having the flag set is enough: a blob with no holes and a single extent is just as slow, and clearing the flag afterwards does not help. Only a fresh dense write does. Signed-off-by: danbugs <danilochiarlone@gmail.com>
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🟡 Changes recommended
It regresses Unix snapshot performance and leaves existing Windows sparse blobs unchanged.
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What changed in this PR
Reverts sparse snapshot blob writes to avoid WHP restore latency.
Changes:
- Restores dense atomic blob writes.
- Removes sparse-write code, tests, and Windows API features.
- Removes the sparse-write changelog entry.
| File | Description |
|---|---|
fsutil.rs |
Restores dense snapshot writes. |
Cargo.toml |
Removes sparse-file API features. |
CHANGELOG.md |
Removes sparse-write documentation. |
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Superseded by #1898 (reopened from a branch in the main repo so CI gets the longer job timeouts). |
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This reverts #1788 because sparse snapshot blobs slow down the first guest function call after a restore on Windows (WHP). Any blob written with `FSCTL_SET_SPARSE` costs about 35 ms extra on that first guest function call, even when the blob has no holes. Clearing the flag later doesn't fix it; only a dense rewrite does. Replaces #1895, which was opened from a fork and hit the shorter CI timeouts. Signed-off-by: danbugs <danilochiarlone@gmail.com>
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This reverts #1788 because sparse snapshot blobs slow down the first guest function call after a restore on Windows (WHP). Any blob written with
FSCTL_SET_SPARSEcosts about 35 ms extra on that first guest function call, even when the blob has no holes. Clearing the flag later doesn't fix it; only a dense rewrite does.