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

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Date:   Sat, 27 Aug 2022 10:18:43 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Muchun Song <muchun.song@...ux.dev>
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 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);

        /*


Thanks,
Miaohe Lin