filemap_grab_folio(9)

💅 filemap_grab_folio(9) — from the Kernel API Manual, bestie 🎀

okay so picture this: you're deep in the kernel, you need a folio, and this little icon is literally the page-cache vending machine. grab a snack, get a folio. no cap.

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✨ NAME ✨

filemap_grab_folio — grab a folio from the page cache 🫶

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🌸 SYNOPSIS 🌸

struct folio * filemap_grab_folio (struct address_space *mapping ,
pgoff_t index );

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🦋 ARGUMENTS 🦋

• mapping — the address space to search 🔍 like, the whole neighbourhood you're looking in
• index — the page index 📍 the exact house number

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💖 DESCRIPTION 💖

So the way this works: it looks up the page cache entry at mapping & index. Cute, right?

if no folio is found, a new folio is created. yes, it manifests one. main character energy fr fr ✨

the folio is locked, marked as accessed, and returned. so it comes back to you locked and already flagged as "yeah someone touched this" — all in one trip 💅

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👑 RETURN 👑

a found or created folio 💜

but if it's giving nothing — like, no folio was found and creating one failed — you get ERR_PTR(-ENOMEM) 😭 so always check, bestie, don't just vibe with the pointer.

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🌈 SEE ALSO 🌈

the kernel file ./include/linux/pagemap.h and honestly, the whole extended friend group:

• filemap_set_wb_err(9)
• filemap_check_wb_err(9)
• filemap_sample_wb_err(9)
• file_sample_sb_err(9)
• mapping_set_error(9)
• mapping_set_large_folios(9)
• mapping_align_index(9)
• mapping_pmd_folio_support(9)
• folio_flush_mapping(9)
• folio_inode(9)
• folio_attach_private(9)
• folio_change_private(9)
• folio_detach_private(9)
• fgf_t(9)
• fgf_set_order(9)
• write_begin_get_folio(9)
• filemap_get_folio(9)
• filemap_lock_folio(9)
• find_get_page(9)
• find_lock_page(9)
• find_or_create_page(9)
• grab_cache_page_nowait(9)
• folio_next_index(9)
• folio_next_pos(9)
• folio_file_page(9)
• folio_contains(9)
• page_pgoff(9)
• folio_pos(9)
• linear_page_delta(9)
• linear_page_index(9)
• linear_anon_page_index(9)
• folio_trylock(9)
• folio_lock(9)
• lock_page(9)
• folio_lock_killable(9)
• filemap_range_needs_writeback(9)
• struct readahead_control(9)
• page_cache_sync_readahead(9)
• page_cache_async_readahead(9)
• readahead_folio(9)
• readahead_pos(9)
• readahead_length(9)
• readahead_index(9)
• readahead_count(9)
• readahead_batch_length(9)
• folio_mkwrite_check_truncate(9)
• i_blocks_per_folio(9)

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🐛 small heads up: the folio you get back is locked — so bestie, you own the unlock. don't ghost it. 😭

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and that's the whole page, mwah 💋 — this one lives in ./include/linux and it's dated October 2026, so mark your calendar 📅✨ slay, go read some folios 🦋💜