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be absolutely sure we have all cases covered, I share that below. I also included information on split. Hopefully this is useful! And maybe we can somehow put in a comment or commit msg or something somewhere? Not sure if a bit much for that though :) Note that in all of the below we hold exclusive mmap, vma + rmap write locks. ## Merge with change to EXISTING VMA ### Merge both start end |<---->| |-------********-------| prev middle next extend delete delete 1. Set prev VMA range [prev->vm_start, next->vmend) 2. Overwrite prev, middle, next nodes in maple tree with prev 3. Detach middle VMA 4. Free middle VMA 5. Detach next VMA 6. Free next VMA ### Merge left full start end |<--------->| |-------************* prev middle extend delete 1. Set prev VMA range [prev->vm_start, end) 2. Overwrite prev, middle nodes in maple tree with prev 3. Detach middle VMA 4. Free middle VMA ### Merge left partial start end |<---->| |-------************* prev middle extend partial overwrite 1. Set prev VMA range [prev->vm_start, end) 2. Set middle range [end, middle->vm_end) 3. Overwrite prev, middle (partial) nodes in maple tree with prev ### Merge right full start end |<--------->| *************-------| middle next delete extend 1. Set next range [start, next->vm_end) 2. Overwrite middle, next nodes in maple tree with next 3. Detach middle VMA 4. Free middle VMA ### Merge right partial start end |<----->| *************-------| middle next shrink extend 1. Set middle range [middle->vm_start, start) 2. Set next range [start, next->vm_end) 3. Overwrite middle (partial), next nodes in maple tree with next ## Merge due to introduction of proposed NEW VMA These cases are easier as there's no existing VMA to either remove or partially adjust. ### Merge both start end |<------>| |-------..........-------| prev (proposed) next extend delete 1. Set prev VMA range [prev->vm_start, next->vm_end) 2. Overwrite prev, next nodes in maple tree with prev 3. Detach next VMA 4. Delete next VMA ### Merge left start end |<------>| |-------.......... prev (proposed) extend 1. Set prev VMA range [prev->vm_start, end) 2. Overwrite prev node in maple tree with newly extended prev (This is what's used for brk() and bprm_mm_init() stack relocation in relocate_vma_down() too) ### Merge right start end |<------>| ..........-------| (proposed) next extend 1. Set next VMA range [start, next->vm_end) 2. Overwrite next node in maple tree with newly extended next ## Split VMA If new below: addr |-----.-----| | new . | |-----.-----| vma Otherwise: addr |-----.-----| | . new | |-----.-----| vma 1. Duplicate vma 2. If new below, set new range to [vma-vm_start, addr) 3. Otherwise, set new range to [addr, vma->vm_end) 4. If new below, Set vma range to [addr, vma->vm_end) 5. Otherwise, set vma range to [vma->vm_start, addr) 6. Partially overwrite vma node in maple tree with new Cheers, Lorenzo