clear_pages(9)

💅 clear_pages — the kernel API manual, bestie edition ✨

okay so this is a page from the Kernel API Manual (that's the manual name, we're just folding it in here 🎀) and it's about clear_pages. Get comfy, this one's short but there are rules.

---

🌸 NAME 🌸

clear_pages — clears a page range for kernel-internal use. That's it, that's the whole job. 💖

---

✨ SYNOPSIS ✨

void clear_pages (void *addr , unsigned int npages );

like. look at her. no return value, she just does it. 💅

---

🫶 ARGUMENTS 🫶

• addr — start address. where the clearing begins, bestie 📍
• npages — number of pages. how many of them we're clearing ✨

---

🦋 DESCRIPTION 🦋

lowkey let me say the most important thing first: if you're clearing a page range that's gonna get mapped to user space, use clear_user_pages instead. not this one. this one is not for that. iykyk 🌈

second thing, and this is the one people forget: it does absolutely no exception handling. none. zero. not a single one. 💀

and here's the vibe check on scheduling — this is the part that gets people, so listen up 👑

even though the clearing operation is preemptible, clear_pages does not call cond_resched to check whether rescheduling is required. and on architectures where it reduces to a few long-running instructions, it might not even be able to. 🫠

so what does that mean for you?

• Under preemptible models? literally not a problem, you're fine, go off 💖
• Under cooperatively scheduled models? different story. the caller is expected to limit npages to no more than PROCESS_PAGES_NON_PREEMPT_BATCH. that's on you, not on her. 🎀

fr fr do not skip the PROCESS_PAGES_NON_PREEMPT_BATCH limit in cooperatively scheduled models. it's not a suggestion, it's the whole contract ✨

---

💜 SEE ALSO 💜

the absolute iconic lineup of friends, all of them, in order, no skips 👑✨:

• Kernel file ./include/linux/mm.h — the file itself, our source of truth 📁
• folio_page_idx(9)
• vma_flag_t(9)
• fault_flag_allow_retry_first(9)
• vma_kernel_pagesize(9)
• folio_order(9)
• folio_reset_order(9)
• folio_mapcount(9)
• folio_mapped(9)
• thp_order(9)
• thp_size(9)
• folio_get(9)
• folio_put(9)
• folio_put_refs(9)
• folios_put(9)
• vma_flags_is_cow_mapping(9)
• vma_is_cow_mapping(9)
• vma_desc_is_cow_mapping(9)
• folio_pfn(9)
• folio_mk_pte(9)
• folio_mk_pmd(9)
• folio_mk_pud(9)
• folio_maybe_dma_pinned(9)
• is_zero_page(9)
• is_zero_folio(9)
• folio_nr_pages(9)
• folio_next(9)
• folio_shift(9)
• folio_size(9)
• folio_maybe_mapped_shared(9)
• folio_expected_ref_count(9)
• zap_vma(9)
• ptdesc_address(9)
• ptdesc_set_kernel(9)
• ptdesc_clear_kernel(9)
• ptdesc_test_kernel(9)
• pagetable_alloc(9)
• pagetable_free(9)
• vma_lookup(9)
• vma_start_pgoff(9)
• vma_end_pgoff(9)
• vma_last_pgoff(9)
• vma_start_anon_pgoff(9)
• vma_end_anon_pgoff(9)
• vma_last_anon_pgoff(9)
• mmap_action_remap(9)
• mmap_action_remap_full(9)
• mmap_action_ioremap(9)
• mmap_action_ioremap_full(9)
• mmap_action_simple_ioremap(9)
• mmap_action_map_kernel_pages(9)
• mmap_action_map_kernel_pages_full(9)
• range_is_subset(9)
• range_in_vma(9)
• range_in_vma_desc(9)

---

okay and that's the page!! 💖 this one lives over in ./include/linux and the date on it is October 2026 — so like, mark your calendar bestie, that's the version you're reading 🎀✨ slay, go clear some pages (kernel-internal ones only, please) 🦋💅