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

[David Hildenbrand]

On 04.02.23 07:18, yang.yang29@xxxxxxxxxx wrote:

[sorry, was on vacation last week]

> > 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).

It adds confusion. Just simplify it please.

> > 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.

Why do we care and make this case special?

--
Thanks,

David / dhildenb