The kernel's reverse-mapping machinery is charged with locating the
page-table entries that refer to a given page in memory.  The reverse
mapping of anonymous pages is handled differently than for file-backed
pages.  The kernel's implementation of reverse mapping for anonymous pages
is, according to Lorenzo Stoakes in his proposal
for a memory-management-track session at the 2026 Linux Storage,
Filesystem, Memory Management, and BPF Summit, "a very broken
abstraction", due to its complexity.  It also has some performance
problems.  Stoakes was there to present, in raw form, a proposed
replacement that he calls a "COW context".

https://lwn.net/Articles/1072378/
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