Re: [PATCHv5 03/28] memcg: adjust to support new THP refcounting

[Vlastimil Babka]

On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> As with rmap, with new refcounting we cannot rely on PageTransHuge() to
> check if we need to charge size of huge page form the cgroup. We need to
> get information from caller to know whether it was mapped with PMD or
> PTE.
>
> We do uncharge when last reference on the page gone. At that point if we
> see PageTransHuge() it means we need to unchange whole huge page.
>
> The tricky part is partial unmap -- when we try to unmap part of huge
> page. We don't do a special handing of this situation, meaning we don't
> uncharge the part of huge page unless last user is gone or
> split_huge_page() is triggered. In case of cgroup memory pressure
> happens the partial unmapped page will be split through shrinker. This
> should be good enough.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

But same question about whether it should be using hpage_nr_pages() 
instead of a constant.

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