lru_cache_drain_for_folio(9)

🌸 NAME — lru_cache_drain_for_folio(9) from the Kernel API Manual 🌸

okay bestie, this page is literally about lru_cache_drain_for_folio — and its whole thing is: drain LRU caches if the caches might hold folio references. 💅✨

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✨ SYNOPSIS ✨

void lru_cache_drain_for_folio (const struct folio *folio , unsigned int
extra_refs , enum lru_cache_drained *drained );

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🫶 ARGUMENTS 🫶

• folio — the folio. 🦋
• extra_refs — extra folio references held by the caller. 💖
• drained — drain status for batch folio processing. 🎀

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💅 DESCRIPTION 💅

okay so the mission is: drain LRU caches if the caches might hold folio references. 👑 It starts with a local LRU cache drain, and then — if local draining was insufficient — it drains LRU caches on all CPUs. that's the escalation arc, no cap. 🔥

Now the detection part: this function detects LRU cache references by comparing the folio refcount with the sum of the expected folio refcount + extra references held by the caller. 🔍 literally comparing refcounts, that's the vibe.

⚠️ and bestie, do not come for PG_lru here: we cannot rely on PG_lru to reliably detect all LRU cache references. there are rare scenarios — concurrent folio (un)mapping) — where this function might miss detecting LRU cache references. 💀 keep that in mind, fr fr.

If drained is not NULL, the function will avoid re-draining LRU caches when processing multiple folios in a row. 🎀 in that case, the variable drained points at must be initialized to LRU_CACHE_NOT_DRAINED before the first invocation by the caller. do not skip the setup, bestie — that's the whole point. 🫶

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🌈 SEE ALSO 🌈

Kernel file ./mm/folio.c:

• folio_mark_accessed(9)
• folio_add_lru(9)
• folio_add_lru_vma(9)
• deactivate_file_folio(9)
• folio_mark_lazyfree(9)
• folios_put_refs(9)
• release_pages(9)
• folio_batch_remove_exceptionals(9)

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💋 mwah! this cutie came from the source ./mm, dated October 2026, and it's literally the lru_cache_drain_for_folio(9) page. periodt. 💅🌸