Add zswap usage and compression meters

[ABHIRAMSHIBU]

Summary

Add Linux zswap visibility to htop without changing existing memory or swap accounting.

This introduces:

• A Zswap bar meter showing compressed pool usage against the configured pool limit.
• A ZswapStats meter showing compressed usage, original size, and compression ratio.
• Detection of zswap being disabled.
• Clear disabled and unavailable states when appropriate.
• Support for systems where the pool limit is unavailable.

The pool limit is derived from the configured max_pool_percent value and total system memory.

Testing

• make -j4
• make check
• git diff --check
• Manually verified zswap-enabled and zswap-disabled states.

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Reviewing files that changed from the base of the PR and between 593a7c8 and fdf6309.

📒 Files selected for processing (6)

• Makefile.am
• linux/LinuxMachine.c
• linux/Platform.c
• linux/ZswapMeter.c
• linux/ZswapMeter.h
• linux/ZswapStats.h

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📝 Walkthrough

Walkthrough

Linux scanning now detects Zswap counters, enablement, and pool limits. Two Linux meter classes display compressed pool usage and compression statistics. Their declarations and implementations are added to the Linux build lists, and both classes are registered in the platform meter registry.

Suggested labels: Linux :penguin:

Suggested reviewers: intelfx, benbe

Poem

Zswap wakes beneath the load,
Counters parse the kernel road.
Pools and ratios take the stage,
Two new meters fill the gauge.
Linux builds the parts in line.

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[coderabbitai]

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⚠️ Outside diff range comments (1)

linux/LinuxMachine.c (1)

249-254: 🚀 Performance & Scalability | 🔵 Trivial | 💤 Low value

Skip max_pool_percent when zswap is disabled. memory_t is 64-bit, so there’s no overflow concern here; the only gain is avoiding an unnecessary sysfs read on the disabled path.

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[BenBE]

LGTM. Only minor notes remaining; nothing critical.

[coderabbitai]

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linux/LinuxMachine.c (1)

162-170: 📐 Maintainability & Code Quality | 🟠 Major | ⚡ Quick win

Avoid adding another function-like macro.

tryReadFlag duplicates parsing logic and hides break control flow inside a macro. Replace it with a small static helper or explicit parsing code in the Z case so the control flow remains visible.

As per coding guidelines, avoid function-like macros.

Source: Coding guidelines

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• linux/LinuxMachine.c
• linux/ZswapMeter.h
• linux/ZswapStats.h

[ABHIRAMSHIBU]

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⚠️ Outside diff range comments (1)

linux/LinuxMachine.c (1)> 162-170: 📐 Maintainability & Code Quality | 🟠 Major | ⚡ Quick win

Avoid adding another function-like macro.
tryReadFlag duplicates parsing logic and hides break control flow inside a macro. Replace it with a small static helper or explicit parsing code in the Z case so the control flow remains visible.
As per coding guidelines, avoid function-like macros.

Source: Coding guidelines

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Initially I was thinking to move it to a function above the current function as LinuxMachine_tryReadFlag(), then felt to duplicate as I didnt know if it was a good idea to do that because it didnt feel right spot to put it after reading the file.

[BenBE]

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Some comments are outside the diff and can’t be posted inline due to platform limitations.
⚠️ Outside diff range comments (1)

linux/LinuxMachine.c (1)> 162-170: 📐 Maintainability & Code Quality | 🟠 Major | ⚡ Quick win

Avoid adding another function-like macro.
tryReadFlag duplicates parsing logic and hides break control flow inside a macro. Replace it with a small static helper or explicit parsing code in the Z case so the control flow remains visible.
As per coding guidelines, avoid function-like macros.

Source: Coding guidelines

ℹ️ Review info

@coderabbitai These function-like macros for parsing are fine when defined for a very limited, local purpose. Copying the existing macro and extending it for the task at hand is fine.

@ABHIRAMSHIBU Can you rebase/squash your commits. Bug fixes to previous parts of a PR should be absorbed into where those issues were introduced.

[coderabbitai]

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@BenBE Understood. Given the established local parsing-macro pattern in linux/LinuxMachine.c, extending it with tryReadFlag is consistent with the surrounding code. I’m withdrawing this comment.

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✏️ Learnings added

Learnt from: BenBE
URL: https://github.com/htop-dev/htop/pull/2047

Timestamp: 2026-07-19T07:54:09.132Z
Learning: In `linux/LinuxMachine.c`, function-like parsing macros with a tightly limited local scope are an accepted project pattern. Extending an existing local parsing macro for related `/proc/meminfo` parsing is preferred over extracting a separate helper solely to avoid duplication.

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