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MEM_LARGE_PAGESflag forVirtualAlloc()). Linux seems to support one or the other but not both at the same, and uses the same word for either case. Note that it's relatively shocking how crippled operating systems are (Windows not supporting 1 GiB pages at all, requiring special permission just to use 2 MiB pages, not allowing 2 MiB pages to be "pageable"; and Linux having a cesspool of hackery with 2 separate systems and no way for user-space to choose)khugepageddoes, unless you disable it withecho 0 >/sys/kernel/mm/transparent_hugepage/khugepaged/defrag. There are some other tune settings to control when an mmap allocation and/or madvise waits for defragging vs. starting with small pages and working in the background. (echo defer+madvise > /sys/kernel/mm/transparent_hugepage/defrag). If you didn't know about this, Linux is less bad than you think!kcompactdis the clue I was missing). It's actually worse/more awful than I suspected - like the name suggests, it literally does "compaction" (moving everything from one end of a physical memory zone to another) rather than only bothering when most small pages belonging to the larger page are already free.