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    SubjectRe: [PATCH 4/8] migrate: add hugepage migration code to move_pages()
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    On Fri, Jul 19, 2013 at 5:34 AM, Naoya Horiguchi
    <n-horiguchi@ah.jp.nec.com> 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 v3:
    > - revert introducing migrate_movable_pages
    > - follow_page_mask(FOLL_GET) returns NULL for tail pages
    > - use isolate_huge_page
    >
    > ChangeLog v2:
    > - updated description and renamed patch title
    >
    > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    > ---
    > mm/memory.c | 12 ++++++++++--
    > mm/migrate.c | 13 +++++++++++--
    > 2 files changed, 21 insertions(+), 4 deletions(-)
    >
    > diff --git v3.11-rc1.orig/mm/memory.c v3.11-rc1/mm/memory.c
    > index 1ce2e2a..8c9a2cb 100644
    > --- v3.11-rc1.orig/mm/memory.c
    > +++ v3.11-rc1/mm/memory.c
    > @@ -1496,7 +1496,8 @@ 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;
    > }
    > @@ -1507,8 +1508,15 @@ 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) {
    > + if (PageHead(page))
    > + get_page_foll(page);
    > + else {
    > + page = NULL;
    > + goto out;
    > + }
    > + }

    Can get_page do the work for us, like the following?

    if (flags & FOLL_GET)
    get_page(page);

    > goto out;
    > }
    > if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
    > diff --git v3.11-rc1.orig/mm/migrate.c v3.11-rc1/mm/migrate.c
    > index 3ec47d3..d313737 100644
    > --- v3.11-rc1.orig/mm/migrate.c
    > +++ v3.11-rc1/mm/migrate.c
    > @@ -1092,7 +1092,11 @@ static struct page *new_page_node(struct page *p, unsigned long private,
    >
    > *result = &pm->status;
    >
    > - return alloc_pages_exact_node(pm->node,
    > + if (PageHuge(p))
    > + return alloc_huge_page_node(page_hstate(compound_head(p)),
    > + pm->node);
    > + else
    > + return alloc_pages_exact_node(pm->node,
    > GFP_HIGHUSER_MOVABLE | GFP_THISNODE, 0);
    > }
    >
    > @@ -1152,6 +1156,11 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
    > !migrate_all)
    > goto put_and_set;
    >
    > + if (PageHuge(page)) {
    > + isolate_huge_page(page, &pagelist);
    > + goto put_and_set;
    > + }
    > +
    > err = isolate_lru_page(page);
    > if (!err) {
    > list_add_tail(&page->lru, &pagelist);
    > @@ -1174,7 +1183,7 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
    > err = migrate_pages(&pagelist, new_page_node,
    > (unsigned long)pm, MIGRATE_SYNC, MR_SYSCALL);
    > if (err)
    > - putback_lru_pages(&pagelist);
    > + putback_movable_pages(&pagelist);
    > }
    >
    > up_read(&mm->mmap_sem);
    > --
    > 1.8.3.1
    >


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