Exercise 2: Total Swap-Used vs. Actively Swapping — Possible Solution
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THE DIFFERENCE
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Per this chapter's warn-box, "a high total swap-used figure can be
historical - memory that was pushed out during an earlier period of
pressure, or proactively swapped out because it was cold and unused,
and simply hasn't been swapped back in since nothing has needed it."
Total swap-used is a cumulative snapshot of memory currently sitting on
disk; it says nothing about whether the system is swapping right now.

THE METRIC THAT DISTINGUISHES THEM
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Per this chapter, "what actually indicates an ongoing, active problem
is vmstat's si and so columns (swap in/out per second) showing
sustained, nonzero movement - not the total figure alone." si and so
measure live swap activity happening at the moment they're checked,
which is a fundamentally different thing from the cumulative total
shown by free -h.

WHY THIS DISTINCTION MATTERS
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A high swap-used total with si/so at or near zero means the system is
not currently under active memory pressure serious enough to be
moving pages in either direction - the swap usage is just sitting
there, unchanged. Only sustained nonzero si/so values indicate memory
is genuinely under active, ongoing pressure right now.

WHY THIS WORKS AS AN ANSWER
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It correctly distinguishes the two concepts (a cumulative total vs. a
live per-second rate), names the specific vmstat columns the chapter
identifies as the actual indicator of active swapping, and explains why
that distinction changes the diagnostic conclusion.