Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 25 Mar 2013 14:36:44 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH 06/10] migrate: add hugepage migration code to move_pages() |
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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-horiguchi@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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