mem_used(9)

💖 mem_used(9) — the Kernel API Manual tea 💖

ok so this is mem_used, a lil function from the Kernel API Manual, and honestly? she's the main character of "how many slots are we even using rn" 💅 let's get into it bestie

---

✨ NAME ✨

mem_used — get number of used slots in an allocator 🎀

like literally, that's her whole job. she counts the used slots. iconic behavior, no notes.

---

🌸 SYNOPSIS 🌸

unsigned long mem_used (struct io_tlb_mem *mem );

that's it. one arg, returns an unsigned long, we love a low-maintenance queen 🫶

---

🦋 ARGUMENTS 🦋

• mem — the Software IO TLB allocator 💖 this is the allocator you're asking about, bestie, so hand her over

---

⭐ DESCRIPTION ⭐

okay so here's the vibe check on how accurate this number actually is, because it depends 👀

• When trace_hiwater and CONFIG_DEBUG_FS is enabled, the result is accurate, because the total number of used slots is tracked in mem->total_used. she's keeping receipts, fr fr 📝
• Otherwise, the result is an approximation, because there is no locking of individual areas. no cap, it's just vibes at that point 🙈

so yeah — sometimes you get the exact count, sometimes you get the spirit of the count 💀

---

🔥 RETURN 🔥

Number of used slots. that's the whole return value, she's not doing extra 💅

---

🌈 SEE ALSO 🌈

Kernel file ./kernel/dma/swiotlb.c plus this whole friend group of functions, all hanging out together 🫶:

• struct io_tlb_slot(9)
• struct io_tlb_area(9)
• swiotlb_adjust_nareas(9)
• limit_nareas(9)
• add_mem_pool(9)
• alloc_dma_pages(9)
• swiotlb_alloc_tlb(9)
• swiotlb_free_tlb(9)
• swiotlb_alloc_pool(9)
• swiotlb_dyn_alloc(9)
• __swiotlb_find_pool(9)
• swiotlb_del_pool(9)
• swiotlb_dev_init(9)
• swiotlb_align_offset(9)
• swiotlb_search_pool_area(9)
• swiotlb_search_area(9)
• swiotlb_find_slots(9)
• mem_pool_used(9)
• swiotlb_tbl_map_single(9)
• swiotlb_del_transient(9)
• is_swiotlb_allocated(9)
• default_swiotlb_base(9)
• default_swiotlb_limit(9)

---

ngl, if you're chasing an exact number, double-check whether trace_hiwater and CONFIG_DEBUG_FS are actually on before you @ her about it 😭

---

💜 and that's the page!! brought to you by ./kernel/dma, dated October 2026 — mwah, go read the source bestie, it's giving essential reading 🧚✨