Exercise 1: Why Low "Free" Next to High "buff/cache" Isn't a Shortage — Possible Solution
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WHY THE KERNEL FILLS SPARE MEMORY WITH CACHE
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Per this chapter, "Linux treats unused RAM as wasted RAM. Rather than
leaving memory sitting empty, the kernel fills it with a cache of
recently-read disk data - the page cache." A low "free" figure on a
machine that's been running for a while is expected behavior, not a
sign of trouble, because the kernel deliberately uses spare capacity
this way.

WHY THE CACHED MEMORY DOESN'T COUNT AS A REAL SHORTAGE
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Per this chapter's finding-box, "cached memory can be dropped almost
instantly the moment an application actually needs that RAM - there's
no cost to reclaiming it, since the same data can simply be re-read
from disk later if needed again." Unlike memory actively held by a
running process, page cache is available to any application that
needs it, essentially for free.

WHAT THIS MEANS FOR READING "FREE" AND "BUFF/CACHE" TOGETHER
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Per this chapter, "a low 'free' number with a large 'buff/cache' number
isn't a shortage at all; it's the kernel using spare capacity
productively, exactly as designed." The two numbers together tell a
positive story - plenty of memory available for genuine reallocation -
rather than the alarming one a bare "free" figure might suggest on its
own.

WHY THIS WORKS AS AN ANSWER
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It explains specifically why the kernel fills unused RAM with cache,
why that cache is reclaimable at essentially no cost, and connects both
points to why the combination of low free/high buff-cache is normal
rather than concerning - rather than treating "free" in isolation.