On Fri 22-03-13 16:23:51, Naoya Horiguchi wrote:
> This patch extends move_pages() to handle vma with VM_HUGETLB set.
> We will be able to migrate hugepage with move_pages(2) after
> applying the enablement patch which comes later in this series.
>
> We avoid getting refcount on tail pages of hugepage, because unlike thp,
> hugepage is not split and we need not care about races with splitting.
>
> And migration of larger (1GB for x86_64) hugepage are not enabled.
>
> ChangeLog v2:
> - updated description and renamed patch title
>
> Signed-off-by: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
> ---
> mm/memory.c | 6 ++++--
> mm/migrate.c | 26 +++++++++++++++++++-------
> 2 files changed, 23 insertions(+), 9 deletions(-)
>
> diff --git v3.9-rc3.orig/mm/memory.c v3.9-rc3/mm/memory.c
> index 494526a..3b6ad3d 100644
> --- v3.9-rc3.orig/mm/memory.c
> +++ v3.9-rc3/mm/memory.c
> @@ -1503,7 +1503,8 @@ struct page *follow_page_mask(struct vm_area_struct
> *vma,
> if (pud_none(*pud))
> goto no_page_table;
> if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
> - BUG_ON(flags & FOLL_GET);
> + if (flags & FOLL_GET)
> + goto out;
> page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
> goto out;
> }
> @@ -1514,8 +1515,9 @@ struct page *follow_page_mask(struct vm_area_struct
> *vma,
> if (pmd_none(*pmd))
> goto no_page_table;
> if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
> - BUG_ON(flags & FOLL_GET);
> page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
> + if (flags & FOLL_GET && PageHead(page))
> + get_page_foll(page);
Hmm, so the caller gets a non-null page without elevated ref counted
even when he asked for it. This means that all callers have to check
PageTail && hugetlb and put_page according to that. That is _really_
fragile.
I think that returning NULL would make more sense in this case.
> goto out;
> }
> if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
> @@ -1164,6 +1175,12 @@ static int do_move_page_to_node_array(struct mm_struct
> *mm,
[...]
> !migrate_all)
> goto put_and_set;
>
> + if (PageHuge(page)) {
> + get_page(page);
> + list_move_tail(&page->lru, &pagelist);
> + goto put_and_set;
> + }
Why do you take an additional reference here? You have one from
follow_page already.
> +
> err = isolate_lru_page(page);
> if (!err) {
> list_add_tail(&page->lru, &pagelist);
[...]
--
Michal Hocko
SUSE Labs
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