[Windows] psutil.swap_memory() shows committed memory instead of swap

[TishSerg]

Summary

• OS: Microsoft Windows [Version 10.0.18363.1379]
• Architecture: AMD64
• Psutil version: 5.8.0
• Python version: 3.8.6
• Type: core

Description

python3.8 -c "import psutil; print(psutil.swap_memory())" shows committed memory (physical memory + pagefile/swap). On FreeBSD, it shows swap only as it should be. I believe on Windows it should show swap-only numbers too (psutil is portable, right?).

[dbwiddis]

On Windows, psutil uses the fields ullTotalPageFile and ullAvailPageFile from MEMORYSTATUSEX but the docs imply those values are associated with the commit limit. To correct using the existing structure, the ullTotalPhys and ullAvailPhys values, respectively, should be subtracted to get swap file usage.

However, MEMORYSTATUSEX only gives a process-level view of memory:

The current committed memory limit for the system or the current process, whichever is smaller, in bytes. To get the system-wide committed memory limit, call GetPerformanceInfo.

This will return a PERFORMANCE_INFORMATION structure. CommitLimit - PhysicalTotal is swap total, and (CommitLimit - CommitTotal) - PhysicalAvailable is swap available.