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SubjectRe: [PATCH v5 03/11] mm: thp: introduce separate TTU flag for thp freezing
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On 04/21/2017 02:17 AM, Zi Yan wrote:
> From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
>
> TTU_MIGRATION is used to convert pte into migration entry until thp split
> completes. This behavior conflicts with thp migration added later patches,
> so let's introduce a new TTU flag specifically for freezing.
>
> try_to_unmap() is used both for thp split (via freeze_page()) and page
> migration (via __unmap_and_move()). In freeze_page(), ttu_flag given for
> head page is like below (assuming anonymous thp):
>
> (TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED | \
> TTU_MIGRATION | TTU_SPLIT_HUGE_PMD)
>
> and ttu_flag given for tail pages is:
>
> (TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED | \
> TTU_MIGRATION)
>
> __unmap_and_move() calls try_to_unmap() with ttu_flag:
>
> (TTU_MIGRATION | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS)
>
> Now I'm trying to insert a branch for thp migration at the top of
> try_to_unmap_one() like below
>
> static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> unsigned long address, void *arg)
> {
> ...
> if (flags & TTU_MIGRATION) {
> if (!pvmw.pte && page) {
> set_pmd_migration_entry(&pvmw, page);
> continue;
> }
> }
>
> , so try_to_unmap() for tail pages called by thp split can go into thp
> migration code path (which converts *pmd* into migration entry), while
> the expectation is to freeze thp (which converts *pte* into migration entry.)
>
> I detected this failure as a "bad page state" error in a testcase where
> split_huge_page() is called from queue_pages_pte_range().
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

It had Kirril's acked-by (https://patchwork.kernel.org/patch/9416221/)
last time around. Please include again.

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