linux-kernel - Re: [RFC PATCH 3/8] hugetlb: create remove_hugetlb

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Date:   Mon, 22 Mar 2021 15:15:43 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Shakeel Butt <shakeelb@...gle.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Rientjes <rientjes@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        HORIGUCHI NAOYA <naoya.horiguchi@....com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Waiman Long <longman@...hat.com>, Peter Xu <peterx@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 3/8] hugetlb: create remove_hugetlb_page() to
 separate functionality

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@...cle.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