From: Muchun Song <muchun.song@linux.dev>
To: "Mika Penttilä" <mpenttil@redhat.com>
Cc: Muchun Song <songmuchun@bytedance.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Memory Management List <linux-mm@kvack.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: hugetlb_vmemmap: use PageCompound() instead of PageReserved()
Date: Wed, 19 Jul 2023 15:00:04 +0800 [thread overview]
Message-ID: <A363D1BA-80B6-4E71-B587-EF04530BBA77@linux.dev> (raw)
In-Reply-To: <2b66797b-3ee9-a70f-25d0-dcab830859d2@redhat.com>
> On Jul 19, 2023, at 14:51, Mika Penttilä <mpenttil@redhat.com> wrote:
>
> Hi,
>
>
> On 19.7.2023 9.31, Muchun Song wrote:
>> The ckeck of PageReserved() is easy to be broken in the future, PageCompound()
>> is more stable to check if the page should be split.
>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>> ---
>> mm/hugetlb_vmemmap.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
>> index 4b9734777f69..8068fe890f52 100644
>> --- a/mm/hugetlb_vmemmap.c
>> +++ b/mm/hugetlb_vmemmap.c
>> @@ -73,8 +73,10 @@ static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
>> * be treated as indepdenent small pages (as they can be freed
>> * individually).
>> */
>> - if (!PageReserved(head))
>> + if (PageCompound(head)) {
>> + VM_BUG_ON(compound_order(head) != get_order(PMD_SIZE));
>> split_page(head, get_order(PMD_SIZE));
>
> I think vmemmap pages are not compound pages (even order > 0).
> They would bug on here trying to split_page() :
You are right. I have missed this. Now I remember why I use
PageReserved() instead of PageCompound() when I fist submit
the commit 39d35edee453. Thanks for your reminder.
Sorry for the noise. Please ignore this patch.
Thanks.
>
>
> void split_page(struct page *page, unsigned int order)
> {
> int i;
>
> VM_BUG_ON_PAGE(PageCompound(page), page);
>
>
>> + }
>> /* Make pte visible before pmd. See comment in pmd_install(). */
>> smp_wmb();
>
> --Mika
>
prev parent reply other threads:[~2023-07-19 7:00 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-19 6:31 [PATCH] mm: hugetlb_vmemmap: use PageCompound() instead of PageReserved() Muchun Song
2023-07-19 6:51 ` Mika Penttilä
2023-07-19 7:00 ` Muchun Song [this message]
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