On 09/25/23 10:12, Mike Kravetz wrote:
> On 09/25/23 21:54, Muchun Song wrote:
> >
> >
> > On 2023/9/25 08:39, Mike Kravetz wrote:
> > > The routine update_and_free_pages_bulk already performs vmemmap
> > > restoration on the list of hugetlb pages in a separate step. In
> > > preparation for more functionality to be added in this step, create a
> > > new routine hugetlb_vmemmap_restore_folios() that will restore
> > > vmemmap for a list of folios.
> > >
> > > This new routine must provide sufficient feedback about errors and
> > > actual restoration performed so that update_and_free_pages_bulk can
> > > perform optimally.
> > >
> > > Special care must be taken when encountering an error from
> > > hugetlb_vmemmap_restore_folios. We want to continue making as much
> > > forward progress as possible. A new routine bulk_vmemmap_restore_error
> > > handles this specific situation.
> > >
> > > Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > > ---
> > > mm/hugetlb.c | 98 +++++++++++++++++++++++++++++++-------------
> > > mm/hugetlb_vmemmap.c | 38 +++++++++++++++++
> > > mm/hugetlb_vmemmap.h | 10 +++++
> > > 3 files changed, 118 insertions(+), 28 deletions(-)
> > >
> > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > > index da0ebd370b5f..53df35fbc3f2 100644
> > > --- a/mm/hugetlb.c
> > > +++ b/mm/hugetlb.c
> > > @@ -1834,50 +1834,92 @@ static void update_and_free_hugetlb_folio(struct hstate *h, struct folio *folio,
> > > schedule_work(&free_hpage_work);
> > > }
> > > -static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
> > > +static void bulk_vmemmap_restore_error(struct hstate *h,
> > > + struct list_head *folio_list,
> > > + struct list_head *non_hvo_folios)
> > > {
> > > struct folio *folio, *t_folio;
> > > - bool clear_dtor = false;
> > > - /*
> > > - * First allocate required vmemmmap (if necessary) for all folios on
> > > - * list. If vmemmap can not be allocated, we can not free folio to
> > > - * lower level allocator, so add back as hugetlb surplus page.
> > > - * add_hugetlb_folio() removes the page from THIS list.
> > > - * Use clear_dtor to note if vmemmap was successfully allocated for
> > > - * ANY page on the list.
> > > - */
> > > - list_for_each_entry_safe(folio, t_folio, list, lru) {
> > > - if (folio_test_hugetlb_vmemmap_optimized(folio)) {
> > > + if (!list_empty(non_hvo_folios)) {
> > > + /*
> > > + * Free any restored hugetlb pages so that restore of the
> > > + * entire list can be retried.
> > > + * The idea is that in the common case of ENOMEM errors freeing
> > > + * hugetlb pages with vmemmap we will free up memory so that we
> > > + * can allocate vmemmap for more hugetlb pages.
> > > + */
> > > + list_for_each_entry_safe(folio, t_folio, non_hvo_folios, lru) {
> > > + list_del(&folio->lru);
> > > + spin_lock_irq(&hugetlb_lock);
> > > + __clear_hugetlb_destructor(h, folio);
> > > + spin_unlock_irq(&hugetlb_lock);
> > > + update_and_free_hugetlb_folio(h, folio, false);
> > > + cond_resched();
> > > + }
> > > + } else {
> > > + /*
> > > + * In the case where there are no folios which can be
> > > + * immediately freed, we loop through the list trying to restore
> > > + * vmemmap individually in the hope that someone elsewhere may
> > > + * have done something to cause success (such as freeing some
> > > + * memory). If unable to restore a hugetlb page, the hugetlb
> > > + * page is made a surplus page and removed from the list.
> > > + * If are able to restore vmemmap and free one hugetlb page, we
> > > + * quit processing the list to retry the bulk operation.
> > > + */
> > > + list_for_each_entry_safe(folio, t_folio, folio_list, lru)
> > > if (hugetlb_vmemmap_restore(h, &folio->page)) {
> >
> > IIUC, the folio should be deleted from the folio list since this
> > huge page will be added to the free list (the list is corrupted),
> > right?
>
> Good catch! Yes, we should remove from the list here.
>
> I did exercise this specific code path and there was no list corruption. In
> any case, I will add the list_del().
Correction. My testing with simulated errors took the else branch here.
--
Mike Kravetz
