linux-kernel - Re: [PATCH v2 4/6] mm: hugetlb: add return -EAGAIN for dissolve_free_huge

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Message-ID: <20210106170754.GU13207@dhcp22.suse.cz>
Date:   Wed, 6 Jan 2021 18:07:54 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        n-horiguchi@...jp.nec.com, ak@...ux.intel.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] mm: hugetlb: add return -EAGAIN for
 dissolve_free_huge_page

On Wed 06-01-21 16:47:37, Muchun Song wrote:
> When dissolve_free_huge_page() races with __free_huge_page(), we can
> do a retry. Because the race window is small.

Is this a bug fix or mere optimization. I have hard time to tell from
the description.
 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  mm/hugetlb.c | 26 +++++++++++++++++++++-----
>  1 file changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
[...]
> @@ -1825,6 +1828,14 @@ int dissolve_free_huge_page(struct page *page)
>  	}
>  out:
>  	spin_unlock(&hugetlb_lock);
> +
> +	/*
> +	 * If the freeing of the HugeTLB page is put on a work queue, we should
> +	 * flush the work before retrying.
> +	 */
> +	if (unlikely(rc == -EAGAIN))
> +		flush_work(&free_hpage_work);

Is it safe to wait for the work to finish from this context?

-- 
Michal Hocko
SUSE Labs