proc_kpageflags(5)

✨ NAME ✨

/proc/kpageflags — physical pages frame masks 💅

okay bestie, welcome to the File Formats Manual, section 5, and today's main character is a lil file in /proc that hands you the receipts on every single physical page frame in your machine. it's giving very much "behind the scenes of your RAM" energy and I'm obsessed.

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🌸 DESCRIPTION 🌸

/proc/kpageflags (since Linux 2.6.25) 🎀

so this file? it's a whole vibe. it contains 64-bit masks corresponding to each physical page frame, and it's indexed by page frame number — like, you wanna know about a page, you look it up by its number, periodt. (for the whole lore on that indexing thing, go read the discussion of /proc/pid/pagemap, iykyk.)

the bits are as follows, and no I did not skip a single one, we do NOT leave bits out in this house 💖:

        0   -   KPF_LOCKED
        1   -   KPF_ERROR
        2   -   KPF_REFERENCED
        3   -   KPF_UPTODATE
        4   -   KPF_DIRTY
        5   -   KPF_LRU
        6   -   KPF_ACTIVE
        7   -   KPF_SLAB
        8   -   KPF_WRITEBACK
        9   -   KPF_RECLAIM
       10   -   KPF_BUDDY
       11   -   KPF_MMAP            (since Linux 2.6.31)
       12   -   KPF_ANON            (since Linux 2.6.31)
       13   -   KPF_SWAPCACHE       (since Linux 2.6.31)
       14   -   KPF_SWAPBACKED      (since Linux 2.6.31)
       15   -   KPF_COMPOUND_HEAD   (since Linux 2.6.31)
       16   -   KPF_COMPOUND_TAIL   (since Linux 2.6.31)
       17   -   KPF_HUGE            (since Linux 2.6.31)
       18   -   KPF_UNEVICTABLE     (since Linux 2.6.31)
       19   -   KPF_HWPOISON        (since Linux 2.6.31)
       20   -   KPF_NOPAGE          (since Linux 2.6.31)
       21   -   KPF_KSM             (since Linux 2.6.32)
       22   -   KPF_THP             (since Linux 3.4)
       23   -   KPF_BALLOON         (since Linux 3.18)
       24   -   KPF_ZERO_PAGE       (since Linux 4.0)
       25   -   KPF_IDLE            (since Linux 4.3)
       26   -   KPF_PGTABLE         (since Linux 4.18)

twenty-seven bits, zero skips, we ate 🍓

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wanna know what each of those lil bits actually means? like, in depth? go peek at the kernel source file Documentation/admin-guide/mm/pagemap.rst 🦋 it's all in there.

⚠️ okay important tea, don't skip this one: before Linux 2.6.29, KPF_WRITEBACK, KPF_RECLAIM, KPF_BUDDY, and KPF_LOCKED did not report correctly. so if you're on something ancient, those four were lowkey lying to you 😭 don't trust them.

🫶 also: the /proc/kpageflags file only even exists if the CONFIG_PROC_PAGE_MONITOR kernel configuration option is enabled. no config, no file, no vibes. simple as that.

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💜 SEE ALSO 💜

• proc(5)

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and that's the whole page, bestie ✨ this was the proc_kpageflags(5) manual, fresh out of Linux man-pages 6.20, dated 2026-02-08 — go forth and vibe check your page frames 💖🎀🦋