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It states: MADV_MERGEABLE (since Linux 2.6.32) Enable Kernel Samepage Merging (KSM) for the pages in the range specified by addr and length. [...] AFAIU, based on code review of ksm_madvise(), this is not strictly true. The KSM implementation enables KSM for pages in the entire vma containing the range. So if it so happens that two mmap areas with identical protection flags are merged, both will be considered mergeable by KSM as soon as at least one page from any of those areas is made mergeable. This does not appear to be an issue in qemu because guard pages with different protection are placed between distinct mappings, which should prevent combining the vmas. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com