> Why use flags if they both conditions are mutually exclusive? Just to make the return value of break_ksm_pmd_entry() more expressive and understandable. because break_ksm_pmd_entry have three types of returned values (0, 1, 2). > MADV_UNMERGEABLE -> unmerge_ksm_pages() will never unshare the shared > zeropage? I thought the patch description mentions that that is one of > the goals? No, MADV_UNMERGEABLE will trigger KSM to unshare the shared zeropages in the context of "get_next_rmap_item() -> unshare_zero_pages(), but not directly in the context of " madvise()-> unmerge_ksm_pages() ". The reason for this is to avoid increasing long delays of madvise() calling on unsharing zero pages.
