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SubjectRe: Freeing HugeTLB page into buddy allocator
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On 04/27/2017 11:24 AM, Naoya Horiguchi wrote:
> On Tue, Apr 25, 2017 at 02:27:27PM +0530, Anshuman Khandual wrote:
>> Hello Jianguo,
>>
>> In the commit a49ecbcd7b0d5a1cda, it talks about HugeTLB page being
>> freed into buddy allocator instead of hugepage_freelists. But if
>> I look the code closely for the function unmap_and_move_huge_page()
>> it only calls putback_active_hugepage() which puts the page into the
>> huge page active list to free up the source HugeTLB page after any
>> successful migration. I might be missing something here, so can you
>> please point me where we release the HugeTLB page into buddy allocator
>> directly during migration ?
>
> Hi Anshuman,
>
> As stated in the patch description, source hugetlb page is freed after
> successful migration if overcommit is configured.
>
> The call chain is like below:
>
> soft_offline_huge_page
> migrate_pages
> unmap_and_move_huge_page
> putback_active_hugepage(hpage)
> put_page // refcount is down to 0
> __put_page
> __put_compound_page
> free_huge_page
> if (h->surplus_huge_pages_node[nid])
> update_and_free_page
> __free_pages
>
> So the inline comment
>
> + /* overcommit hugetlb page will be freed to buddy */
>
> might be confusing because at this point the overcommit hugetlb page was
> already freed to buddy.
>
> I hope this will help you.

Surely does. Thanks Naoya.

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