isolate_single_pageblock(9)

💅 NAME

isolate_single_pageblock — bestie, this one genuinely tries to isolate a pageblock that might be sitting inside a free page or an in-use page. Like, it's out here doing the work 💖

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✨ SYNOPSIS

int isolate_single_pageblock (unsigned long boundary_pfn , enum
pb_isolate_mode mode , bool isolate_before , bool skip_isolation );

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🎀 ARGUMENTS

• boundary_pfn — a pageblock-aligned pfn that a page might cross. Like the line in the sand, okurrr 🌸
• mode — the isolation mode. That's it, that's the whole vibe 🦋
• isolate_before — isolate the pageblock before the boundary_pfn. Yes, the one that comes first 💅
• skip_isolation — the flag to skip the pageblock isolation in second isolate_single_pageblock. It's giving "second time around, we're not doing that again" 🙈

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🌈 DESCRIPTION

So here's the tea, bestie: free and in-use pages can be as big as MAX_PAGE_ORDER, and they can contain more than one pageblock. Not a big deal, right? Wrong. 😭 When not all pageblocks within a page are isolated at the same time, free page accounting can go wrong. Like, actually wrong. The math stops mathing.

For example — and stay with me here — in the case of MAX_PAGE_ORDER = pageblock_order + 1, a MAX_PAGE_ORDER page has two pageblocks. Two. Not one. Two. 💀

[      MAX_PAGE_ORDER         ] [  pageblock0  |  pageblock1  ]

When either pageblock is isolated, if it's a free page, the page is not split into separate migratetype lists, which is supposed to happen. Rude. And if it's an in-use page and gets freed later, __free_one_page does not split the free page either. Double rude. 😤

The function handles all of this by splitting the free page, or migrating the in-use page and then splitting the free page. That's the whole assignment, and it ate 🔥👑

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🧚 SEE ALSO

• Kernel file ./mm/page_isolation.c
• start_isolate_page_range(9)
• undo_isolate_page_range(9)
• test_pages_isolated(9)

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okay that's the whole page bestie, go forth and isolate responsibly 🫶✨

this icon of a page lives in ./mm and it's dated October 2026 — no cap, that's literally what the footer said, mwah 💜