linux-kernel - Re: [PATCH 08/10] hugetlb: remove unneeded SetHPageVmemmapOptimized()

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Date:   Sat, 27 Aug 2022 10:56:40 +0800
From:   Muchun Song <muchun.song@...ux.dev>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Linux MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/10] hugetlb: remove unneeded SetHPageVmemmapOptimized()



> On Aug 27, 2022, at 10:18, Miaohe Lin <linmiaohe@...wei.com> wrote:
> 
> On 2022/8/27 9:35, Muchun Song wrote:
>> 
>> 
>>> On Aug 26, 2022, at 17:24, Miaohe Lin <linmiaohe@...wei.com> wrote:
>>> 
>>> If code reaches here, it's guaranteed that HPageVmemmapOptimized is set
>>> for the hugetlb page (or VM_BUG_ON_PAGE() will complain about it). It's
>> 
>> Hi Miaohe,
>> 
>> Right.
>> 
>>> unnecessary to set it again.
>> 
>> No, I suppose you didn’t test this patch since it does not work. The
>> HPageVmemmapOptimized is cleared in the above code of line
>> (set_page_private(page, 0)). So NAck.
> 
> Sorry, I missed that and thanks for pointing this out. Does this code deserves a
> comment like below?
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index d0617d64d718..3374c1d2b52e 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1522,6 +1522,10 @@ static void add_hugetlb_page(struct hstate *h, struct page *page,
> 
>        set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
>        set_page_private(page, 0);
> +       /*
> +        * We have to set HPageVmemmapOptimized again as above
> +        * set_page_private(page, 0) cleared it.
> +        */
>        SetHPageVmemmapOptimized(page);

I’m fine with this comment.

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


> 
>        /*
> 
> 
> Thanks,
> Miaohe Lin