Re: [RFC PATCH 3/8] hugetlb: create remove_hugetlb_page() to separate functionality

Michal Hocko
2021-03-22T14:16:34Z

On Fri 19-03-21 15:42:04, Mike Kravetz wrote:
> The new remove_hugetlb_page() routine is designed to remove a hugetlb
> page from hugetlbfs processing. It will remove the page from the active
> or free list, update global counters and set the compound page
> destructor to NULL so that PageHuge() will return false for the 'page'.
> After this call, the 'page' can be treated as a normal compound page or
> a collection of base size pages.
>
> remove_hugetlb_page is to be called with the hugetlb_lock held.
>
> Creating this routine and separating functionality is in preparation for
> restructuring code to reduce lock hold times.

I like this! Counters handling both in __free_huge_page and
update_and_free_page is really confusing.

> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
> mm/hugetlb.c | 70 ++++++++++++++++++++++++++++++++++------------------
> 1 file changed, 46 insertions(+), 24 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index c537274c2a38..ae185d3315e0 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1306,6 +1306,46 @@ static inline void destroy_compound_gigantic_page(struct page *page,
> unsigned int order) { }
> #endif
>
> +/*
> + * Remove hugetlb page from lists, and update dtor so that page appears
> + * as just a compound page. A reference is held on the page.
> + * NOTE: hugetlb specific page flags stored in page->private are not
> + * automatically cleared. These flags may be used in routines
> + * which operate on the resulting compound page.
> + *
> + * Must be called with hugetlb lock held.
> + */
> +static void remove_hugetlb_page(struct hstate *h, struct page *page,
> + bool adjust_surplus)
> +{
> + int nid = page_to_nid(page);
> +

I think we want lockdep_assert_held here. Lockdep asserts are not used
in this code but now that you are touching it then it is probably better
to start adding them. What do you think?

> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
> + return;
> +
> + list_del(&page->lru);
> +
> + if (HPageFreed(page)) {
> + h->free_huge_pages--;
> + h->free_huge_pages_node[nid]--;
> + ClearHPageFreed(page);
> + }
> + if (adjust_surplus) {
> + h->surplus_huge_pages--;
> + h->surplus_huge_pages_node[nid]--;
> + }
> +
> + VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
> + VM_BUG_ON_PAGE(hugetlb_cgroup_from_page_rsvd(page), page);
> +
> + ClearHPageTemporary(page);
> + set_page_refcounted(page);
> + set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
> +
> + h->nr_huge_pages--;
> + h->nr_huge_pages_node[nid]--;
> +}

--
Michal Hocko
SUSE Labs