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Subject: Re: [PATCH v2 2/2] hugetlb: optimize update_and_free_pages_bulk to
 avoid lock cycles
From:   Muchun Song <muchun.song@linux.dev>
In-Reply-To: <20230718004942.113174-3-mike.kravetz@oracle.com>
Date:   Wed, 19 Jul 2023 11:35:44 +0800
Cc:     Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jiaqi Yan <jiaqiyan@google.com>,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        Muchun Song <songmuchun@bytedance.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        James Houghton <jthoughton@google.com>,
        Michal Hocko <mhocko@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>
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References: <20230718004942.113174-1-mike.kravetz@oracle.com>
 <20230718004942.113174-3-mike.kravetz@oracle.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Precedence: bulk


> On Jul 18, 2023, at 08:49, Mike Kravetz <mike.kravetz@oracle.com> wrote:
> 
> update_and_free_pages_bulk is designed to free a list of hugetlb pages
> back to their associated lower level allocators.  This may require
> allocating vmemmmap pages associated with each hugetlb page.  The
> hugetlb page destructor must be changed before pages are freed to lower
> level allocators.  However, the destructor must be changed under the
> hugetlb lock.  This means there is potentially one lock cycle per page.
> 
> Minimize the number of lock cycles in update_and_free_pages_bulk by:
> 1) allocating necessary vmemmap for all hugetlb pages on the list
> 2) take hugetlb lock and clear destructor for all pages on the list
> 3) free all pages on list back to low level allocators
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.