wip(blocks): a BAM flush reads and writes only the pages that hold the volume's bits (#155) [skip ci]

Browse Source

Not yet accepted. bam_flush_to_disk() and bam_sync_from_disk() read and
wrote every page of the BAM; with the stick's BAM sized for 256 GiB (6144
devblocks, 24 MiB) every flush of a dirty block moved 24 MiB each way.
They now touch only the pages that hold the slot's bits -- its reserved
bits and one per user block (bam_pages_used()) -- the pages past them are
never set, so the bytes on disk are the same.

Test (qemu_session.py bam_flush, --target qemu-stick --stick-gib 16):
three SAVE-BUFFERS of an Artemis block, each timed, then the BAM hashed.
Before: 5.1 / 5.6 / 6.1 s (the 2 s limit fails; it was set after seeing
this baseline). After: 1.1 / 1.1 / 1.1 s. The BAM's bytes the same either
way: sha256 79197a40...b9e44b50, 5 non-zero bytes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GE3SDvQn5EoxdGufk84zz2

...

This commit is contained in:

Claude

2026-11-08 14:21:57 +00:00

parent b399cb7c35

commit 52f48ed2a9

6 changed files with 412 additions and 7 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download Patch File Download Diff File Expand all files Collapse all files

experiments/bare_metal/runs/doe-amd64-20261108-141717.csv

experiments/bare_metal/runs/doe-amd64-20261108-141943.csv