folio_try_s...non_rmap_pmd(9)

📦 version 7.3.1, in nixpkgs unstable

💅 folio_try_share_anon_rmap_pmd — the Kernel API Manual, section 9 ✨

okay so bestie, welcome to page nine of the Kernel API Manual, and today's main character is folio_try_share_anon_rmap_pmd 🎀 she's a little function with a big name and she has ONE job, but it's lowkey an important one, so let's get into it.

🌸 NAME 🌸

folio_try_share_anon_rmap_pmd — try marking an exclusive anonymous page range mapped by a PMD possibly shared to prepare for temporary unmapping 💅

like, yes, that is the whole name, yes it's a mouthful, no we are not shortening it, periodt.

✨ SYNOPSIS ✨

int folio_try_share_anon_rmap_pmd (struct folio *folio , struct page
*page );

look at her go 🫶 returns an int, takes a struct folio *folio and a struct page *page, and honestly the int return is the whole plot twist here, iykyk.

🦋 ARGUMENTS 🦋

  • folio — the folio whose mapping we're sharing. she's the vibe, she's the subject of the whole operation 💖
  • page — the first page whose mapping we're sharing. first one, not just any one, not the middle one — the first. 🙈

🔥 DESCRIPTION 🔥

okay so the page range of the folio is defined by [page, page + HPAGE_PMD_NR) — that's the window we're working with, and no, it is not negotiable ✨

the caller needs to hold the page table lock and has to have the page table entries cleared/invalidated. both. not one, not the other. both. this is not a drill 🚨

she's similar to folio_try_dup_anon_rmap_pmd, BUT — and this is the tea ☕ — she is not used during fork to duplicate a mapping. instead, she's used to prepare for temporarily unmapping parts of a folio (swap, migration) via folio_remove_rmap_pmd. so like, same energy, different purpose. got it? good 💅

marking the mapped pages shared can only fail if the folio maybe pinned. and device private folios cannot get pinned, and consequently this function cannot fail. not "probably won't" — cannot. iconic honestly 👑

so the return situation is:

  • returns 0 if marking the mapped pages possibly shared succeeded ✅
  • returns -EBUSY otherwise 😭

that's it, that's the API. two outcomes, zero drama (unless it's -EBUSY, then a little drama).

💜 SEE ALSO 💜

kernel file ./include/linux/rmap.h and her whole friend group:

go read those too, bestie, you'll be so smart, I promise 🧚

reminder bestie: hold the page table lock, clear/invalidate those page table entries, and remember that -EBUSY is a real answer, not a personal attack 💀

that's the page!! this one came from ./include/linux (the kernel file ./include/linux/rmap.h), dated October 2026, living in section 9 of the Kernel API Manual — mwah, slay, go read some more rmap functions, ily 🍓💖✨

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