The 15 GB kernel run completed with every phase mark under budget, but
the budget metric itself -- the charged footprint the extract gate reads
on every file pull -- reached 16.8 GB. Two defects, found with a probe at
the gate (one line per 256 MB of charge after the spill latch, with the
class table; mem.charge.probe, CBM_MEM_PHASES=1, stays in).
Worker graph buffers kept a dense id array over the global id space. The
charge climbed gradually from the 14.06 GB latch to 14.96 GB, then jumped
about 1 GB between two consecutive gate reads, and the only class that
moved in that step was gbuf_index. Worker buffers draw ids from the shared
counter, so each of the 18 kept an id -> node array spanning the whole
global id space -- 8.5M ids x 8 B, next power of two -- almost entirely
empty, and when the global id crossed 2^23 all eighteen doubled in the
same instant. Nothing asks a worker buffer by id before the merge (every
cbm_gbuf_find_by_id caller runs on the main buffer); the worker
constructor now drops the array the way it already drops the five
secondary indexes, and the main buffer answers by id after the merge.
Spill mode did not park what was already cached. The sweeps ran only on an
over-budget observation; a run that latched early (near_budget) and then
stayed under budget through extraction -- which is exactly what the first
fix produced: 14,949 MB at the extract mark -- carried the 44,797 results
cached before the latch (8 GB) into registry build and resolve, which
cannot park, and resolve ran at a charged 21.8 GB against the 15 GB
budget with nothing to stop it. The earlier runs only fitted because the
id-array burst tripped the sweeps by accident. Extraction now ends with a
final sweep whenever spill mode is on: results belong on disk before the
phases that cannot park inherit them.
Kernel, CBM_MEM_BUDGET_MB=15000, before -> after: charged high-water
16,771-16,818 MB -> 14,582 and 14,732 MB in two runs (97-98% of the
budget); the final sweep parks ~45k results and takes the charge from
14.6 to 4.3 GB before resolve, which peaks at 11.5 GB committed; wall
234 -> 224-230 s; nodes identical (8,529,729), edges inside the
run-to-run band. RSS high-water 18.7 GB is
pages already purged and not yet reclaimed: the footprint never exceeds
7.3 GB at a mark.
peak_charged_mb (7b77fd48) is what made this measurable: the kernel at
the default budget reads charged 22.3 GB against 24.6 GB while ps reports
29 GB RSS, and the 15 GB run read 16.8 GB where every mark was under.
Tests: gbuf_worker_buffer_keeps_no_by_id_array (graph_buffer: one node at
id 2M in a worker buffer must not grow the index class by even 1 MB where
the dense array costs 16 MB; the worker answers by QN, the main buffer by
id after the merge) -- RED on the dense array, GREEN without it.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
Martin Vogel
a2f29b3fe7