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Subject: Re: [PATCH 08/10] hugetlb: remove unneeded SetHPageVmemmapOptimized()
To:     Muchun Song <muchun.song@linux.dev>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Linux MM <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
References: <20220826092422.39591-1-linmiaohe@huawei.com>
 <20220826092422.39591-9-linmiaohe@huawei.com>
 <A1ED2200-136D-477E-B1EC-E61E6B75931B@linux.dev>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <e367da7d-7964-7531-3dcb-0ad7964ffdaa@huawei.com>
Date:   Sat, 27 Aug 2022 10:18:43 +0800
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On 2022/8/27 9:35, Muchun Song wrote:
> 
> 
>> On Aug 26, 2022, at 17:24, Miaohe Lin <linmiaohe@huawei.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);

        /*


Thanks,
Miaohe Lin