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b=oAHXisBDzimhXI17wnijGsm4Kj3KwqSSO3NGUOdLz+1w/SMlJbxfKDEcFUM+LzsFH yXZvH7lyhU+H/wQ7YtPQU6R1mIluNmEQJfGAQhC03AFHfmzoYgeIaRcCv5U+NIU77Y xDivJB30dZqPvS+pEFcaZmZrUhsmIEtM4HoaWdZqXxZoTaVYXBUMhB/U9n4GQarLcq SBzJOAhGGVluqLFboRvbHyctyXlY2waiys128tJ5SLSt+OyOM4Rn6Acxvrqj7z5pvQ VljWqC1Oyjx0aGmqK2NgPK1nwwoZ3j4gsd0WUlN8K1CtgK/AzhuDQu4KN6pq6NFeYs foSUkoiGRL5OQ== Message-ID: Date: Tue, 28 Apr 2026 21:36:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages To: Lance Yang Cc: dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, rppt@kernel.org, jgg@ziepe.ca, baolu.lu@linux.intel.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org References: <20260428-vmemmap-v1-1-b2aa1e6db2c0@kernel.org> <20260428132025.86657-1-lance.yang@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 71608100013 X-Rspamd-Server: rspam06 X-Stat-Signature: qqpnayrz835rb3tcgs4z8duhfsmfmbe3 X-HE-Tag: 1777405027-571919 X-HE-Meta: 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 3KNbPIe1 aEXhzAaEL/7ZFgh40N1TLv12mJEpNiLxO3CD8ofvM++bOKx1g6zwWNH9+ifIIPCfCXWLyKDdXNBj4ZjerA1RC35TMD9GBLA8HVJ3HZgK3lc1CRCFIm268lbKurJcJKXF/gz6CEucIpHFExyn0nRUoAwX+s1mWA0yHXzPCMvmLW3GBPslPooNabbyRaAubY/i3oP/rExUcFwuWC78zcu+l5pbJmRKrJAUvKsl9bBgrvmf98ZGVrvvQMRR9Hf561pmwlKxzBaQto5yxfRhBJKdFn0zef3BF5E6Je3Ce Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/28/26 15:20, Lance Yang wrote: > > On Tue, Apr 28, 2026 at 12:29:36PM +0200, David Hildenbrand (Arm) wrote: >> In commit bf9e4e30f353 ("x86/mm: use pagetable_free()"), we switched >>from freeing non-boot page tables through __free_pages() to >> pagetable_free(). >> >> However, the function is also called to free vmemmap pages. >> >> Given that vmemmap pages are not page tables, already the page_ptdesc(page) >> is wrong. But worse, pagetable_free() calls >> >> __free_pages(page, compound_order(page)); >> >> As vmemmap pages are not compound pages (see vmemmap_alloc_block()) -- >> except for HVO, which doesn't apply here -- we will only free the first >> page when freeing a PMD-sized vmemmap page, leaking the other ones. >> >> Fix it by properly decoupling pagetable and vmemmap freeing. >> free_pagetable() no longer has to mess with SECTION_INFO, as only the >> vmemmap is marked like that in register_page_bootmem_memmap(). >> >> While at it, just wire up the altmap parameter for remove_pte_table(). >> Also, the indentation in remove_pmd_table() is messed up, let's fix that >> while touching it. >> >> Note that we'll try to get rid of that bootmem info handling soon. For >> now, we'll handle it similar to free_pagetable(), just avoiding the >> ifdef. >> >> Fixes: bf9e4e30f353 ("x86/mm: use pagetable_free()") >> Cc: stable@vger.kernel.org >> Signed-off-by: David Hildenbrand (Arm) >> --- >> Reproduced and tested with a simple VM with a virtio-mem device, >> repeatedly adding and removing memory. >> >> Found by code inspection while working on bootmem_info removal. >> --- > > Cool! I just reproduced the leak with QEMU pc-dimm memory hotplug as > well. > > Without the fix, nr_free_pages kept dropping after the hotplugged memory > was removed again. With the fix applied, it stays stable over repeated > add/remove cycles :) > > Tested-by: Lance Yang Thanks Lance! I'll wait a bit more for feedback, and then resend v2 with the "nr_pages" simplification. -- Cheers, David