__mem_cgroup..._charge_swap(9)

💅 __mem_cgroup..._charge_swap(9) — like, the Kernel API Manual page, bestie

okay so. this is a page out of the Kernel API Manual, and the function it's hyping up is __mem_cgroup_try_charge_swap. yes the page title is the truncated one with the ... in it, that's just how the kernel do. anyway it's short, it's sweet, and it's lowkey doing a very specific job. let's get into it 🫶

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✨ NAME ✨

__mem_cgroup_try_charge_swap — literally "try charging swap space for a folio". that's the whole vibe. it tries. if it works, slay. if not, it tells you. 💸

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🌸 SYNOPSIS 🌸

int __mem_cgroup_try_charge_swap (struct folio *folio );

one argument, one int coming back at you. no cap, that's it. ✨

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🎀 ARGUMENTS 🎀

• folio — the folio that's being added to swap. this is the main character of the whole call, the thing getting charged. 👑

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💖 DESCRIPTION 💖

so here's the tea ☕ — this function tries to charge the folio's memcg (that's the memory cgroup it belongs to, iykyk) for the swap space sitting at folio->swap.

"tries" is doing a lot of heavy lifting in that sentence and honestly? iconic. because it can fail.

returns 0 on success — everything went great, no notes, perfect. 🎉

returns -ENOMEM on failure — as in, no memory to go around, the charge did not go through, and you gotta deal with it. 😭

that's genuinely the entire behaviour. short king of a function. 👑

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🦋 SEE ALSO 🦋

this page lives in the kernel file ./mm/memcontrol.c, and it's rolling with a whole friend group of related pages. genuinely a group chat. here's every single one, no skips, no "etc." — periodt 💅

• get_mem_cgroup_css_from_folio(9)
• page_cgroup_ino(9)
• lruvec_page_state_monotonic(9)
• mod_memcg_state(9)
• mod_lruvec_state(9)
• count_memcg_events(9)
• get_mem_cgroup_from_mm(9)
• get_mem_cgroup_from_current(9)
• get_mem_cgroup_from_folio(9)
• mem_cgroup_iter(9)
• mem_cgroup_iter_break(9)
• mem_cgroup_scan_tasks(9)
• folio_lruvec_lock(9)
• folio_lruvec_lock_irq(9)
• folio_lruvec_lock_irqsave(9)
• mem_cgroup_update_lru_size(9)
• mem_cgroup_margin(9)
• mem_cgroup_print_oom_context(9)
• mem_cgroup_print_oom_meminfo(9)
• mem_cgroup_get_oom_group(9)
• consume_stock(9)
• __memcg_kmem_charge_page(9)
• __memcg_kmem_uncharge_page(9)
• mem_cgroup_wb_stats(9)
• mem_cgroup_from_private_id(9)
• mem_cgroup_css_reset(9)
• mem_cgroup_calculate_protection(9)
• mem_cgroup_charge_hugetlb(9)
• mem_cgroup_swapin_charge_folio(9)
• mem_cgroup_replace_folio(9)
• mem_cgroup_migrate(9)
• mem_cgroup_sk_charge(9)
• mem_cgroup_sk_uncharge(9)
• __mem_cgroup_uncharge_swap(9)
• obj_cgroup_may_zswap(9)
• obj_cgroup_charge_zswap(9)
• obj_cgroup_uncharge_zswap(9)

like, go read some of those too. they're right there. 🧚

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real talk though bestie: this one only tries to charge. if you get -ENOMEM back, that's not a "huh weird" moment, that's the whole point — handle it. 💀

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🌈 cute sign-off 🌈

and that's the page!! 💜 it ships out of ./mm and it's dated October 2026 — so yeah, mark your calendars, time-travelling kernel manpage era. go charge some swap, bestie. 🍓