anon_vma_clone(9)

💅 anon_vma_clone — from the Kernel API Manual, bestie 🎀

okay so picture this: you're deep in the kernel, you've got a VMA, and its anon_vma_chain is literally empty. tragic. this function is the glow-up. ✨

✨ NAME ✨

anon_vma_clone — it builds brand-new anon_vma_chain objects inside @dst that link to all the anon_vma objects sitting inside @src's anon_vma_chains. no cap, all of them. 🫶

🦋 SYNOPSIS 🦋

int anon_vma_clone (struct vm_area_struct *dst , struct vm_area_struct *src , enum vma_operation operation );

🌸 ARGUMENTS 🌸

• dst — the destination VMA. its anon_vma_chain is empty — like, zero notes, empty fridge, nothing. that's the vibe we're starting from. 🍓
• src — the source VMA. this is the one we're wishing to duplicate. it's the main character, dst is getting the makeover. 💖
• operation — the type of operation that resulted in the clone. yes, we're nosy about why we got called. 👀

👑 DESCRIPTION 👑

this is, like, the heart of the VMA side of the anon_vma implementation?? every single time we need to set up a new VMA's anon_vma state, we roll up with this function. it's giving backbone. it's giving foundation. periodt. 🔥

here's when it gets invoked:

• VMA Merge — but only when dst is unfaulted and src is faulted, meaning we clone src into dst. conditional queen. 💅
• VMA split ✂️
• VMA (m)remap 🗺️
• Fork of faulted VMA 🍴

in all cases other than fork, this is simply a duplication. like, copy-paste, no thoughts head empty. fork is the extra one though — fork additionally adds a new active anon_vma. not me, not fork, being the overachiever. 😭

and here's the spicy bit: ONLY in the case of fork do we try to 'reuse' existing anon_vma's in an anon_vma hierarchy — reusing anon_vma's that have no VMA associated with them but do have a single child. why? to avoid waste of memory when repeatedly forking. sustainability icon. recycle that memory, bestie 🌈♻️

⭐ RETURN ⭐

• 0 on success — slay 💅
• -ENOMEM on failure — she ran out of memory, it happens to the best of us 😭

🧚 SEE ALSO 🧚

Kernel file ./mm/rmap.c — __anon_vma_prepare(9), unlink_anon_vmas(9), page_address_in_vma(9), folio_referenced(9), mapping_wrprotect_range(9), pfn_mkclean_range(9), folio_move_anon_rmap(9), __folio_set_anon(9), __page_check_anon_rmap(9), folio_add_anon_rmap_ptes(9), folio_add_anon_rmap_pmd(9), folio_add_new_anon_rmap(9), folio_add_file_rmap_ptes(9), folio_add_file_rmap_pmd(9), folio_add_file_rmap_pud(9), folio_remove_rmap_ptes(9), folio_remove_rmap_pmd(9), folio_remove_rmap_pud(9), try_to_unmap(9), try_to_migrate(9), make_device_exclusive(9), __rmap_walk_file(9)

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that's the whole page bestie, go read the source now, iykyk 💜

okay and one last thing before you close the tab: this little masterpiece lives in ./mm, and the version-and-date stamp on it is October 2026. so like… future icon behavior honestly. 🦋✨ bye bestie, mwah 🫶💖