gmap_helper_discard(9)

💅 gmap_helper_discard — a gmap_helper_discard(9) moment

okay so bestie, welcome to gmap_helper_discard, straight out of section 9 of the Kernel API Manual. no cap, this one is short but it's doing something. let's get into it 🎀

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✨ NAME ✨

gmap_helper_discard — literally discards user pages in the given range. that's the whole vibe 🦋

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✨ SYNOPSIS ✨

void gmap_helper_discard (struct mm_struct *mm , unsigned long vmaddr ,
       unsigned long end );

like, copy it exactly, spaces and all, don't @ me 💅

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✨ ARGUMENTS ✨

• mm — the mm. yes. that's the description. it's giving "main character energy" but the character is an mm_struct 😭
• vmaddr — the starting userspace address. where the party begins 🎉
• end — the end address, aka the first address outside the range. so it's not invited to the party, it's the bouncer at the door 🙈

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✨ DESCRIPTION ✨

so, ALL the userspace pages hanging out in the range [vamddr, end) get discarded and unmapped. gone. not invited back. periodt 💀✨

(yes, vamddr — that's exactly how it's spelled in the original, and I am simply not the one who's gonna fix it. we respect the text 🫶)

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✨ CONTEXT ✨

important bestie, listen: this needs to be called while holding the mmap lock. like, you cannot just roll up without it. that's the whole dress code 🔒👑

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✨ SEE ALSO ✨

go be nosy in the kernel file ./arch/s390/mm/gmap_helpers.c and also check out the whole friend group:

• try_get_locked_pte(9)
• gmap_helper_zap_one_page(9)
• gmap_helper_try_set_pte_unused(9)
• gmap_helper_disable_cow_sharing(9)

all of them? iconic. no notes 🌈

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and that's the page!! 💖 this whole thing comes to you from ./arch/s390/mm, dated October 2026, and it's from the Kernel API Manual era of the man pages. mwah, go hold that mmap lock, love u, bye 🍓🧚💜