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From: Muchun Song In-Reply-To: <2b66797b-3ee9-a70f-25d0-dcab830859d2@redhat.com> Date: Wed, 19 Jul 2023 15:00:04 +0800 Cc: Muchun Song , Mike Kravetz , Andrew Morton , Linux Memory Management List , linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20230719063132.37676-1-songmuchun@bytedance.com> <2b66797b-3ee9-a70f-25d0-dcab830859d2@redhat.com> To: =?utf-8?Q?Mika_Penttil=C3=A4?= X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 56D8B1C002A X-Rspam-User: X-Stat-Signature: 1xafox931mmqh6n3cq5hz59h7jbm5y7e X-Rspamd-Server: rspam03 X-HE-Tag: 1689750048-542937 X-HE-Meta: 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 lQ3oSO6l mM2Pyz4t8GpTSWIqr4N2VK1XbTGkOB+zUrL+lsZd3BSPBwdNypPSJwan+eyiwGcGjc1dwCflNQEe+3U+vtVpp98XG/z7UIT3UmEPo+8ZE4GA2Bd6/7/4iqlrV/k/pvgsqg71anWJ7NZxbAZB5/QzMmFzI9Y1C9qi0+33KAi5+HopyvuKCpZudQWsNdRyzcvh7z6zEddzI5GX70YwaJu2q98Xn8g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Jul 19, 2023, at 14:51, Mika Penttil=C3=A4 = wrote: >=20 > Hi, >=20 >=20 > 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 >> --- >> 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) !=3D get_order(PMD_SIZE)); >> split_page(head, get_order(PMD_SIZE)); >=20 > 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. >=20 >=20 > void split_page(struct page *page, unsigned int order) > { > int i; >=20 > VM_BUG_ON_PAGE(PageCompound(page), page); >=20 >=20 >> + } >> /* Make pte visible before pmd. See comment in pmd_install(). */ >> smp_wmb(); >=20 > --Mika >=20