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SubjectRe: [External] Re: [PATCH v21 0/9] Free some vmemmap pages of HugeTLB page
On Thu, Apr 29, 2021 at 10:32 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 4/28/21 5:26 AM, Muchun Song wrote:
> > On Wed, Apr 28, 2021 at 7:47 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
> >>
> >> Thanks! I will take a look at the modifications soon.
> >>
> >> I applied the patches to Andrew's mmotm-2021-04-21-23-03, ran some tests and
> >> got the following warning. We may need to special case that call to
> >> __prep_new_huge_page/free_huge_page_vmemmap from alloc_and_dissolve_huge_page
> >> as it is holding hugetlb lock with IRQs disabled.
> >
> > Good catch. Thanks Mike. I will fix it in the next version. How about this:
> >
> > @@ -1618,7 +1617,8 @@ static void __prep_new_huge_page(struct hstate
> > *h, struct page *page)
> >
> > static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
> > {
> > + free_huge_page_vmemmap(h, page);
> > __prep_new_huge_page(page);
> > spin_lock_irq(&hugetlb_lock);
> > __prep_account_new_huge_page(h, nid);
> > spin_unlock_irq(&hugetlb_lock);
> > @@ -2429,6 +2429,7 @@ static int alloc_and_dissolve_huge_page(struct
> > hstate *h, struct page *old_page,
> > if (!new_page)
> > return -ENOMEM;
> >
> > + free_huge_page_vmemmap(h, new_page);
> > retry:
> > spin_lock_irq(&hugetlb_lock);
> > if (!PageHuge(old_page)) {
> > @@ -2489,7 +2490,7 @@ static int alloc_and_dissolve_huge_page(struct
> > hstate *h, struct page *old_page,
> >
> > free_new:
> > spin_unlock_irq(&hugetlb_lock);
> > - __free_pages(new_page, huge_page_order(h));
> > + update_and_free_page(h, new_page, false);
> >
> > return ret;
> > }
> >
> >
>
> Another option would be to leave the prep* routines as is and only
> modify alloc_and_dissolve_huge_page as follows:

OK. LGTM. I will use this. Thanks Mike.

>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 9c617c19fc18..f8e5013a6b46 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2420,14 +2420,15 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
>
> /*
> * Before dissolving the page, we need to allocate a new one for the
> - * pool to remain stable. Using alloc_buddy_huge_page() allows us to
> - * not having to deal with prep_new_huge_page() and avoids dealing of any
> - * counters. This simplifies and let us do the whole thing under the
> - * lock.
> + * pool to remain stable. Here, we allocate the page and 'prep' it
> + * by doing everything but actually updating counters and adding to
> + * the pool. This simplifies and let us do most of the processing
> + * under the lock.
> */
> new_page = alloc_buddy_huge_page(h, gfp_mask, nid, NULL, NULL);
> if (!new_page)
> return -ENOMEM;
> + __prep_new_huge_page(h, new_page);
>
> retry:
> spin_lock_irq(&hugetlb_lock);
> @@ -2473,7 +2474,6 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
> * Reference count trick is needed because allocator gives us
> * referenced page but the pool requires pages with 0 refcount.
> */
> - __prep_new_huge_page(h, new_page);
> __prep_account_new_huge_page(h, nid);
> page_ref_dec(new_page);
> enqueue_huge_page(h, new_page);
> @@ -2489,7 +2489,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
>
> free_new:
> spin_unlock_irq(&hugetlb_lock);
> - __free_pages(new_page, huge_page_order(h));
> + update_and_free_page(h, old_page, false);
>
> return ret;
> }
>
> --
> Mike Kravetz

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