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    SubjectRe: [PATCH 03/10] soft-offline: use migrate_pages() instead of migrate_huge_page()
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    Michal Hocko <mhocko@suse.cz> writes:

    > On Tue 26-03-13 16:59:40, Aneesh Kumar K.V wrote:
    >> Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> writes:
    > [...]
    >> > diff --git v3.9-rc3.orig/mm/memory-failure.c v3.9-rc3/mm/memory-failure.c
    >> > index df0694c..4e01082 100644
    >> > --- v3.9-rc3.orig/mm/memory-failure.c
    >> > +++ v3.9-rc3/mm/memory-failure.c
    >> > @@ -1467,6 +1467,7 @@ static int soft_offline_huge_page(struct page *page, int flags)
    >> > int ret;
    >> > unsigned long pfn = page_to_pfn(page);
    >> > struct page *hpage = compound_head(page);
    >> > + LIST_HEAD(pagelist);
    >> >
    >> > /*
    >> > * This double-check of PageHWPoison is to avoid the race with
    >> > @@ -1482,12 +1483,20 @@ static int soft_offline_huge_page(struct page *page, int flags)
    >> > unlock_page(hpage);
    >> >
    >> > /* Keep page count to indicate a given hugepage is isolated. */
    >> > - ret = migrate_huge_page(hpage, new_page, MPOL_MF_MOVE_ALL,
    >> > - MIGRATE_SYNC);
    >> > - put_page(hpage);
    >> > + list_move(&hpage->lru, &pagelist);
    >>
    >> we use hpage->lru to add the hpage to h->hugepage_activelist. This will
    >> break a hugetlb cgroup removal isn't it ?
    >
    > This particular part will not break removal because
    > hugetlb_cgroup_css_offline loops until hugetlb_cgroup_have_usage is 0.
    >
    > Little bit offtopic:
    > Btw. hugetlb migration breaks to charging even before this patchset
    > AFAICS. The above put_page should remove the last reference and then it
    > will uncharge it but I do not see anything that would charge a new page.
    > This is all because regula LRU pages are uncharged when they are
    > unmapped. But this a different story not related to this series.


    But when we call that put_page, we would have alreayd move the cgroup
    information to the new page. We have

    h_cg = hugetlb_cgroup_from_page(oldhpage);
    set_hugetlb_cgroup(oldhpage, NULL);

    /* move the h_cg details to new cgroup */
    set_hugetlb_cgroup(newhpage, h_cg);


    in hugetlb_cgroup_migrate

    -aneesh



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