darwin: exclude inactive and speculative pages from used memory

[natoscott]

Inactive and speculative pages are reclaimable caches, not actively used memory. Counting them as "used" inflates the displayed value far beyond what Activity Monitor reports, especially on high-RAM Apple Silicon systems (e.g. 49G vs 9G on a 192GB M2 Ultra).

Both classes already had countsAsCache=true; this change sets countsAsUsed=false so they no longer contribute to the "used" total. They remain visible when "Show cached memory" is enabled.

Resolves: #1975

[SuhasSrinivasan]

@natoscott
Sorry, the fix does not seem to be working in the high-memory Mac.
It appears to be reporting Wired Memory: 2.55G/192G.
Please see below

$ vm_stat | perl -ne '/page size of (\d+)/ and $size=$1; /Pages\s+([^:]+)[^\d]+(\d+)/ and printf("%-16s % 16.2f Mi\n", "$1:", $2 * $size / 1048576);'
free:                      220.58 Mi
active:                  11399.62 Mi
inactive:               181134.55 Mi
speculative:               104.58 Mi
throttled:                   0.00 Mi
wired down:               2538.06 Mi
purgeable:                  84.17 Mi
copy-on-write:          415799.92 Mi
zero filled:           1984858.75 Mi
reactivated:              1366.33 Mi
purged:                  61407.42 Mi
stored in compressor:           243.97 Mi
occupied by compressor:            68.73 Mi

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 172555d2-aed9-474a-98cd-39d47b498c0a

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Reviewing files that changed from the base of the PR and between 9dc8009 and af53de4.

📒 Files selected for processing (2)

• configure.ac
• darwin/Platform.c

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📝 Walkthrough

Summary

Surgically fixes macOS memory accounting that inflated "used" memory on high‑RAM Apple Silicon systems by reclassifying page types and switching to the correct page-count source for anonymous/app pages.

Changes

• configure.ac: add autoconf check for struct vm_statistics64.internal_page_count (AC_CHECK_MEMBERS).
• darwin/Platform.c:
  • Memory classes: set speculative and inactive to countsAsUsed=false while retaining countsAsCache=true (they remain visible when "Show cached memory" is enabled).
  • Platform_setMemoryValues: prefer vm->internal_page_count (when available) and compute Active = page_K * saturatingSub(internal_page_count, vm->purgeable_count). Inactive and speculative are nonzero only when showCachedMemory is enabled. Fallback to vm->active_count if internal_page_count is unavailable.

Assessment

• Implementation is focused and minimal: only a build-time availability probe and the Darwin memory-class/metric computations were changed.
• Logic aligns with Activity Monitor semantics (anonymous/app pages counted as active/app memory; inactive/speculative treated as cache).
• Backward compatibility preserved via fallback when internal_page_count is missing.
• Commit is cohesive and scoped; changes are small and reviewable.

Note

Reviewer feedback indicates a report where large inactive counts still appear and displayed wired/used values remained unexpected on a high‑memory Mac; follow-up testing on affected hardware is recommended.

Walkthrough

This PR updates macOS memory reporting: configure.ac now detects vm_statistics64.internal_page_count; Platform.c marks speculative and inactive pages as cache-only (countsAsUsed=false) and selects internal_page_count (or active_count fallback). Memory-class calculations for ACTIVE now use page_K * saturatingSub(internal_page_count, vm->purgeable_count); INACTIVE and SPECULATIVE are tied to showCachedMemory and PURGEABLE uses vm->purgeable_count when shown.

Assessment against linked issues

Objective	Addressed	Explanation
Fix incorrect memory usage reporting on macOS (#1975)	✅
Use correct VM statistics field instead of external_page_count (#1975)	✅
Adjust memory class accounting for speculative/inactive pages (#1975)	✅

Poem

Where internal counts replace a ghostly tide,
Active trimmed by purgeable on the side,
Speculative and inactive step out of use,
Numbers settle true, no more obtuse,
Quiet metrics sing: the meter’s right.

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_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

Actionable comments posted: 1

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 2ad74dcb-56e9-456e-ad5b-b4409d26c982

📥 Commits

Reviewing files that changed from the base of the PR and between b7f9df9 and 9dc8009.

📒 Files selected for processing (2)

• configure.ac
• darwin/Platform.c

[SuhasSrinivasan]

Thank you, tested and confirming that new fix af53de4 reports as 15.1 G / 192 G.

htop dropped from the buggy 48 G down to 15.1 G.