prepare_highmem_image(9)

💖 prepare_highmem_image(9) 💖

okay so bestie, welcome to the prepare_highmem_image page from the Kernel API Manual — yes that's the manual name, it's giving very serious kernel energy and honestly? iconic. sit down, grab a snack 🍓, we're learning about allocating memory for loading highmem data from an image. no cap.

---

✨ NAME ✨

prepare_highmem_image — allocate memory for loading highmem data from image. that's it, that's the whole vibe. 🫶

---

🌸 SYNOPSIS 🌸

int prepare_highmem_image (struct memory_bitmap *bm , unsigned int
*nr_highmem_p );

look at her. so clean. so signature. 💅

---

🎀 ARGUMENTS 🎀

• bm — pointer to an uninitialized memory bitmap structure. bestie, note the word uninitialized — this is not a "oops I forgot to init it" situation, that's the whole assignment. 👀
• nr_highmem_p — pointer to the number of highmem image pages. it's a pointer, so it's pointing at the variable holding that count. 🦋

---

🔥 DESCRIPTION 🔥

okay so here's what she does: prepare_highmem_image tries to allocate as many highmem pages as there are highmem image pages. and where does it get that number? nr_highmem_p points to the variable containing the number of highmem image pages. iykyk.

the pages that are "safe" — and by "safe" we mean they will not be overwritten when the hibernation image is restored entirely 😭 — get the corresponding bits set in bm.

and bm must be uninitialized. literally the requirement. don't come in here with a pre-baked bitmap, that's not the move. 🙈

---

💀 NOTE 💀

do not call this function if there are no highmem image pages. like, at all. fr fr. this is not a drill, this is the documented note and we respect it. 🚫

---

🌈 SEE ALSO 🌈

kernel file ./kernel/power/snapshot.c — and the whole friend group, all of them, no one gets left out:

• get_image_page(9)
• free_image_page(9)
• alloc_rtree_node(9)
• free_mem_extents(9)
• create_mem_extents(9)
• memory_bm_next_pfn(9)
• mark_nosave_pages(9)
• create_basic_memory_bitmaps(9)
• free_basic_memory_bitmaps(9)
• snapshot_additional_pages(9)
• count_free_highmem_pages(9)
• count_highmem_pages(9)
• count_data_pages(9)
• swsusp_free(9)
• preallocate_image_pages(9)
• free_unnecessary_pages(9)
• minimum_image_size(9)
• hibernate_preallocate_memory(9)
• pack_pfns(9)
• snapshot_read_next(9)
• unpack_orig_pfns(9)
• count_highmem_image_pages(9)
• copy_last_highmem_page(9)
• prepare_image(9)
• snapshot_write_next(9)
• restore_highmem(9)

---

and that's the page, bestie — you ate that. this one lives under ./kernel/power and it's dated October 2026. mwah 💜✨