proc_pid_clear_refs(5)

💖 proc_pid_clear_refs(5) — the girlies' guide 💖

ok so this is a page from the File Formats Manual, bestie, and it's all about one very specific little file. let's get into it 🫶

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✨ NAME ✨

/proc/pid/clear_refs — reset the PG_Referenced and ACCESSED/YOUNG bits

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🌸 DESCRIPTION 🌸

/proc/pid/clear_refs (since Linux 2.6.22)

okay so first thing, the vibe check: this is a write-only file. you can't read it, no ma'am. and it's writable only by the owner of the process — so like, it's giving exclusive, invite-only energy. 💅

here's what you can write to it:

• 1 (since Linux 2.6.22) — reset the PG_Referenced and ACCESSED/YOUNG bits for all the pages associated with the process. 🫶

🚨 lore drop: before Linux 2.6.32, writing any nonzero value to this file had this exact effect. so like, back then, 7 and 1 were the same thing, no cap.

• 2 (since Linux 2.6.32) — reset the PG_Referenced and ACCESSED/YOUNG bits for all the anonymous pages associated with the process.
• 3 (since Linux 2.6.32) — reset the PG_Referenced and ACCESSED/YOUNG bits for all the file-mapped pages associated with the process.

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🦋 why would you even do that tho 🦋

clearing the PG_Referenced and ACCESSED/YOUNG bits gives you a method to measure approximately how much memory a process is using. it's a whole little ritual and honestly it slays:

1. first, you go inspect the values in the "Referenced" fields for the VMAs shown in /proc/pid/smaps — that gives you an idea of the memory footprint of the process. ✨
2. then you clear the PG_Referenced and ACCESSED/YOUNG bits, and after some measured time interval, you go inspect those "Referenced" fields again — that gives you an idea of the change in memory footprint of the process during the measured interval. 💫

and if you're only interested in inspecting the selected mapping types? then you can use the value 2 or 3 instead of 1. periodt. 🎀

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👑 further values (yes, there's more) 👑

• 4 (since Linux 3.11) — clear the soft-dirty bit for all the pages associated with the process. this one is used, in conjunction with /proc/pid/pagemap, by the check-point restore system to discover which pages of a process have been dirtied since the file /proc/pid/clear_refs was written to. iykyk 🧚
• 5 (since Linux 4.0) — reset the peak resident set size (the "high water mark", iconic name tbh) to the process's current resident set size value. 📉

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💀 the fine print (important, bestie, don't skip) 💀

writing any value to /proc/pid/clear_refs other than those listed above has no effect. literally nothing happens. the file is not gagged, it's just unbothered. 🙈

alsoooo: the /proc/pid/clear_refs file is present only if the CONFIG_PROC_PAGE_MONITOR kernel configuration option is enabled. no config option, no file, no ~vibes~. 👑

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🌈 SEE ALSO 🌈

• proc(5) — the mothership, the main character, go read her 🫶

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written up in Linux man-pages 6.20, dated 2026-02-08, for all my proc_pid_clear_refs(5) girlies — stay hydrated, clear your bits, and remember: write-only means write-only 💜✨