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Fri, 05 Dec 2025 21:56:06 -0800 (PST) Received: from localhost.localdomain ([2403:2c80:6::3077]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29daeaab9c0sm65407775ad.68.2025.12.05.21.56.00 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 05 Dec 2025 21:56:06 -0800 (PST) From: Lance Yang To: david@kernel.org Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, aneesh.kumar@kernel.org, arnd@arndb.de, harry.yoo@oracle.com, jannh@google.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, liushixin2@huawei.com, loberman@redhat.com, lorenzo.stoakes@oracle.com, muchun.song@linux.dev, nadav.amit@gmail.com, npiggin@gmail.com, osalvador@suse.de, peterz@infradead.org, pfalcato@suse.de, prakash.sangappa@oracle.com, riel@surriel.com, stable@vger.kernel.org, vbabka@suse.cz, will@kernel.org, Lance Yang Subject: Re: [PATCH v1 1/4] mm/hugetlb: fix hugetlb_pmd_shared() Date: Sat, 6 Dec 2025 13:55:53 +0800 Message-ID: <20251206055553.21759-1-ioworker0@gmail.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20251205213558.2980480-2-david@kernel.org> References: <20251205213558.2980480-2-david@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: z19fzm8y3igqmnmquyit4odbo8y4bozz X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: CCDB640004 X-HE-Tag: 1765000567-811301 X-HE-Meta: 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 1e45LDbo 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 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: List-Subscribe: List-Unsubscribe: From: Lance Yang On Fri, 5 Dec 2025 22:35:55 +0100, David Hildenbrand (Red Hat) wrote: > We switched from (wrongly) using the page count to an independent > shared count. Now, shared page tables have a refcount of 1 (excluding > speculative references) and instead use ptdesc->pt_share_count to > identify sharing. > > We didn't convert hugetlb_pmd_shared(), so right now, we would never > detect a shared PMD table as such, because sharing/unsharing no longer > touches the refcount of a PMD table. > > Page migration, like mbind() or migrate_pages() would allow for migrating > folios mapped into such shared PMD tables, even though the folios are > not exclusive. In smaps we would account them as "private" although they > are "shared", and we would be wrongly setting the PM_MMAP_EXCLUSIVE in the > pagemap interface. > > Fix it by properly using ptdesc_pmd_is_shared() in hugetlb_pmd_shared(). > > Fixes: 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count") > Cc: > Cc: Liu Shixin > Signed-off-by: David Hildenbrand (Red Hat) > --- Good catch! Feel free to add: Reviewed-by: Lance yang > include/linux/hugetlb.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index 019a1c5281e4e..03c8725efa289 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -1326,7 +1326,7 @@ static inline __init void hugetlb_cma_reserve(int order) > #ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING > static inline bool hugetlb_pmd_shared(pte_t *pte) > { > - return page_count(virt_to_page(pte)) > 1; > + return ptdesc_pmd_is_shared(virt_to_ptdesc(pte)); > } > #else > static inline bool hugetlb_pmd_shared(pte_t *pte)