doc/manual/rl-next: mention symbol value reuse

Forgotten in the symbol value reuse chain.

Change-Id: I7050f56cffcddce5fae4f74ebb35a9fe108a5dcf
Signed-off-by: Raito Bezarius <raito@lix.systems>

doc/manual/change-authors.yml

@@ -158,6 +158,10 @@ midnightveil:
   forgejo: midnightveil
   github: midnightveil
 
+nan-git:
+  display_name: NaN-git
+  github: NaN-git
+
 ncfavier:
   github: ncfavier
 

doc/manual/rl-next/symbol-value-reuse.md

@@ -0,0 +1,32 @@
+---
+synopsis: Symbols reuses once-allocated Value to reduce garbage collected allocations
+issues: []
+cls: [3308, 3300, 3314, 3310, 3312, 3313]
+category: Improvements
+credits: [raito, horrors, thubrecht, nan-git]
+---
+
+In the Lix evaluator, **symbols** represent immutable strings, like those used
+for attribute names.
+
+In evaluator design, such strings are typically [**interned**](https://en.wikipedia.org/wiki/String_interning), stored uniquely
+to save memory, and Lix inherits this approach from the original C++ codebase.
+
+However, some builtins, like `builtins.attrNames`, must return a `Value` type
+that can represent any Nix value (strings, integers, lists, etc.).
+
+Before this change, these builtins would create lists of `Value` objects by
+allocating them through the garbage collector, copying the symbol’s string
+content each time.
+
+This allocation is unnecessary if the interned symbols themselves also hold a
+`Value` representation allocated outside the garbage collector, since these
+live for the full duration of evaluation.
+
+As a result, this reduces the number of allocations, leading to:
+
+* A significant drop in maximum [resident set memory](https://en.wikipedia.org/wiki/Resident_set_size) (RSS), with some large-scale
+  tests showing up to 11% (about 500 MiB) savings in large colmena deployments.
+* A slight decrease in CPU usage during Nix evaluations.
+
+This change is inspired by https://github.com/NixOS/nix/pull/13258 but the approach is different.