STRUCT IO_TLB_MEM(9)

✨ struct io_tlb_mem(9) ✨

okay so bestie, welcome to the Kernel API Manual 💖 — today's main character is struct io_tlb_mem, which is literally the Software IO TLB allocator. yes it's a struct, yes it's iconic, yes you're gonna understand it. periodt 🫶

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🌸 NAME 🌸

struct io_tlb_mem — the Software IO TLB allocator, no cap 💅

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🦋 SYNOPSIS 🦋

struct io_tlb_mem {
    struct io_tlb_pool defpool;
    unsigned long nslabs;
    struct dentry *debugfs;
    bool force_bounce;
    bool for_alloc;
    bool cc_shared;
  #ifdef CONFIG_SWIOTLB_DYNAMIC;
    bool can_grow;
    u64 phys_limit;
    spinlock_t lock;
    struct list_head pools;
    struct work_struct dyn_alloc;
  #endif;
  #ifdef CONFIG_DEBUG_FS;
    atomic_long_t total_used;
    atomic_long_t used_hiwater;
    atomic_long_t transient_nslabs;
  #endif;
 };

like, look at her. she's got conditional compilation AND vibes ✨

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🎀 Members 🎀

okay so here's the breakdown, member by member, and I need you to stay with me because every single one matters 💜

• defpool — the default (initial) IO TLB memory pool descriptor. the og pool, the blueprint, the moment 🫶
• nslabs — total number of IO TLB slabs in all pools. yes, all of them, she's counting everything 💅
• debugfs — the dentry to debugfs. that's it, that's the member ✨
• force_bounce — true if swiotlb bouncing is forced 🔥
• for_alloc — true if the pool is used for memory allocation
• cc_shared — true if the pool memory is shared for confidential computing 👑
• can_grow — true if more pools can be allocated dynamically 🌱
• phys_limit — maximum allowed physical address. the ceiling, the limit, the boundary bestie 🚧
• lock — lock to synchronize changes to the list. no racing, no chaos, we're civilized here 🔒
• pools — list of IO TLB memory pool descriptors (if dynamic)
• dyn_alloc — dynamic IO TLB pool allocation work. she's working, she's busy, respect it 💀
• total_used — the total number of slots in the pool that are currently used across all areas. used only for calculating used_hiwater via boot parameter swiotlb=track_hiwater and exposed via debugfs 👀
• used_hiwater — the high water mark for total_used. can be enabled at boot time via swiotlb=track_hiwater and exposed via debugfs 🌊
• transient_nslabs — the total number of slots in all transient pools that are currently used across all areas. short-lived but still counting herself 📊

ngl, if you're poking at total_used or used_hiwater outside of the swiotlb=track_hiwater boot parameter / debugfs situation, that's not the vibe the struct intended 🙈 they're literally described as used only for that and exposed via debugfs.

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🌈 SEE ALSO 🌈

• Kernel file ./include/linux/swiotlb.h struct io_tlb_pool(9), swiotlb_find_pool(9) 🦋

go read those next, iykyk ⭐

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and that's the whole page bestie!! 🍓 this one lives in ./include/linux and the version/date on the tin is October 2026 — so like, future-dated documentation, main character energy fr fr 🧚💜 mwah, go read your kernel headers 💅✨