STRUCT KSM_RMAP_ITEM(9)

💖 NAME 💖

okay bestie, welcome to struct ksm_rmap_item(9) from the Kernel API Manual — this one is literally the reverse mapping item for virtual addresses. yep, that's the whole vibe. 🫶

✨ SYNOPSIS ✨

no cap, here's the exact shape of it:

struct ksm_rmap_item {
    struct ksm_rmap_item *rmap_list;
    union {
      struct anon_vma *anon_vma;
  #ifdef CONFIG_NUMA;
      int nid;
  #endif;
    };
    struct mm_struct *mm;
    unsigned long address;
    union {
      struct {
        unsigned int oldchecksum;
        rmap_age_t age;
        rmap_age_t remaining_skips;
      };
      unsigned long linear_page_index;
    };
    union {
      struct rb_node node;
      struct {
        struct ksm_stable_node *head;
        struct hlist_node hlist;
      };
    };
 };

🫶 Members 🫶

• rmap_list — the next rmap_item in mm_slot's singly-linked rmap_list. linked-list bestie behavior, fr fr. 🔗
• {unnamed_union} — anonymous. no name, just mystery. 🙈
  • anon_vma — pointer to anon_vma for this mm,address, when in stable tree. 👀
  • nid — NUMA node id of unstable tree in which linked (may not match page). noted, bestie.
• mm — the memory structure this rmap_item is pointing into. 🧠
• address — the virtual address this rmap_item tracks (+ flags in low bits). yes, the low bits are doing their own little thing. ✨
• {unnamed_union} — anonymous. again. iconic. 💅
  • {unnamed_struct} — anonymous.
    • oldchecksum — previous checksum of the page at that virtual address. 🧾
    • age — number of scan iterations since creation (unstable node). ⏳
    • remaining_skips — how many scans to skip (unstable node). okay skip queen. 💀
  • linear_page_index — the original page's index before merged by KSM (stable node). 📌
• {unnamed_union} — anonymous. one more for the road. 🌈
  • node — rb node of this rmap_item in the unstable tree. 🌳
  • {unnamed_struct} — anonymous.
    • head — pointer to stable_node heading this list in the stable tree. 👑
    • hlist — link into hlist of rmap_items hanging off that stable_node. 🪝

🔍 SEE ALSO 🔍

• Kernel file ./mm/ksm.c Overview(9)
• struct ksm_mm_slot(9)
• struct ksm_scan(9)
• struct ksm_stable_node(9)
• struct advisor_ctx(9)
• replace_page(9)
• ksm_do_scan(9)
• ksm_vma_flags(9)
• ksm_enable_merge_any(9)
• ksm_disable_merge_any(9)

Source/version vibes: ./mm · date: October 2026 · manual: struct ksm_rmap_item(9). that's the footer, bestie — bye! 💖🎀