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Subject: Re: [PATCH v7 4/7] mm,hugetlb: Split prep_new_huge_page functionality
To:     Oscar Salvador <osalvador@suse.de>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>,
        Michal Hocko <mhocko@kernel.org>,
        Muchun Song <songmuchun@bytedance.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <20210413104747.12177-1-osalvador@suse.de>
 <20210413104747.12177-5-osalvador@suse.de>
From:   Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <94992151-03fc-dedd-3e09-811908d26d04@oracle.com>
Date:   Tue, 13 Apr 2021 14:33:41 -0700
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On 4/13/21 3:47 AM, Oscar Salvador wrote:
> Currently, prep_new_huge_page() performs two functions.
> It sets the right state for a new hugetlb, and increases the hstate's
> counters to account for the new page.
> 
> Let us split its functionality into two separate functions, decoupling
> the handling of the counters from initializing a hugepage.
> The outcome is having __prep_new_huge_page(), which only
> initializes the page , and __prep_account_new_huge_page(), which adds
> the new page to the hstate's counters.
> 
> This allows us to be able to set a hugetlb without having to worry
> about the counter/locking. It will prove useful in the next patch.
> prep_new_huge_page() still calls both functions.
> 
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> ---
>  mm/hugetlb.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index e40d5fe5c63c..0607b2b71ac6 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1483,7 +1483,16 @@ void free_huge_page(struct page *page)
>  	}
>  }
>  
> -static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
> +/*
> + * Must be called with the hugetlb lock held
> + */
> +static void __prep_account_new_huge_page(struct hstate *h, int nid)
> +{
> +	h->nr_huge_pages++;
> +	h->nr_huge_pages_node[nid]++;

I would prefer if we also move setting the destructor to this routine.
	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);

That way, PageHuge() will be false until it 'really' is a huge page.
If not, we could potentially go into that retry loop in
dissolve_free_huge_page or alloc_and_dissolve_huge_page in patch 5.
-- 
Mike Kravetz

> +}
> +
> +static void __prep_new_huge_page(struct page *page)
>  {
>  	INIT_LIST_HEAD(&page->lru);
>  	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
> @@ -1491,9 +1500,13 @@ static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
>  	set_hugetlb_cgroup(page, NULL);
>  	set_hugetlb_cgroup_rsvd(page, NULL);
>  	ClearHPageFreed(page);
> +}
> +
> +static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
> +{
> +	__prep_new_huge_page(page);
>  	spin_lock_irq(&hugetlb_lock);
> -	h->nr_huge_pages++;
> -	h->nr_huge_pages_node[nid]++;
> +	__prep_account_new_huge_page(h, nid);
>  	spin_unlock_irq(&hugetlb_lock);
>  }
>  
>