Re: [PATCH v5 2/6] ksm: support unsharing zero pages placed by KSM

[yang.yang29]

> 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.