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b=gifK1Ti/VgNSex0l9sLQuUuZpqcdPVUpCa5aG1GjioAJxNHU9wnKrZuzvodrfce5o +2fMUkRg8wVr9tLGihB9hRmgu2LdPyMeLpzwfG8f4FI3hLloTDVfiJOmkQA59klUdD xPnrsyUjuVfKruR8NR2jiRDVPaIHiL9WP6z8N1Z+4IeClzGWGDbwg4gjKyV4qoxp6v 8hDcXinuFA39qRkmfkC6UoGpU00pHf/19pnNKtB4o5o5Zk7RxHtfz6vHqxsWl3k2TG lBtDw1xdUV5GaeHgFs07tXbu9uXpOQDVmJTT1N01przGF7zo/YhP0bDKf+yBUWpyV6 Il4A8a9nGgqJA== Message-ID: <38919e81-4c35-4e8b-ba2a-8af8be60b0b6@kernel.org> Date: Mon, 6 Jul 2026 11:13:45 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 2/8] mm: factor zone-device page init helpers out of __init_zone_device_page To: Li Zhe , akpm@linux-foundation.org, apopple@nvidia.com, arnd@arndb.de, bp@alien8.de, dave.hansen@linux.intel.com, kees@kernel.org, mingo@redhat.com, rppt@kernel.org, tglx@kernel.org Cc: linux-arch@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org References: <20260701090553.62691-1-lizhe.67@bytedance.com> <20260701090553.62691-3-lizhe.67@bytedance.com> 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-Server: rspam04 X-Rspamd-Queue-Id: 5638420003 X-Stat-Signature: ts1heth3ooqdb36qdrujgj1m8a5kt5rq X-HE-Tag: 1783329233-944407 X-HE-Meta: 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 +Z3HZJIL S6cvDEMXbXxLwfaWOsbzAfPRTln4vG9cJjP/u0CTs56a6zaiIgBpAaCN5nXyqzuMdsMHMO2OnukSav03Mzi6ftyMplAo7DqsmhYd2FOOyxPujlSOxyXXNiwR8/+Cm6T2ZYG4B3Lhrhv98lVO8qfjmuKqF97nLkve8Rz2Jb6ZEhkw9tvjCDFoB/24+RqkqLSpEINN5M7QG4u8ScSEi12DgROFJW3y0I/jCr8liEdH+lvvV4Gg81wXovDxwarUOf9XcJScqp6d+yUwJwD78FHiAxg4sqr1xUrs5DEzCZ/gpN0UXHWJiMQRrAg0CT6ORjIT97xnpw3sGbCcN5xfsL8gNTVBPKP0wsy2YManS Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/1/26 11:05, Li Zhe wrote: > memmap_init_zone_device() currently mixes refcount policy and core > ZONE_DEVICE page setup in a single helper. > > Factor the refcount-reset predicate into pagemap_resets_refcount(), move > the common page initialization into __zone_device_page_init(), and wrap > the existing slow path in zone_device_page_init_slow(). > > This keeps the slow-path behaviour unchanged and gives later patches > reusable helper boundaries. > > No functional change intended. > > Signed-off-by: Li Zhe > Reviewed-by: Mike Rapoport (Microsoft) > --- > mm/mm_init.c | 57 ++++++++++++++++++++++++++++++++++------------------ > 1 file changed, 38 insertions(+), 19 deletions(-) > > diff --git a/mm/mm_init.c b/mm/mm_init.c > index 95808ab5cfdb..4c7fad440c2a 100644 > --- a/mm/mm_init.c > +++ b/mm/mm_init.c > @@ -1005,11 +1005,38 @@ static void __init memmap_init(void) > } > > #ifdef CONFIG_ZONE_DEVICE > -static void __ref __init_zone_device_page(struct page *page, unsigned long pfn, > +/* > + * Return true when the free path for this pagemap type restores the page > + * refcount to 1, so memmap_init_zone_device() can keep the count set by > + * __init_single_page(). Otherwise initialize the refcount to 0 and leave > + * it to the allocator or pgmap callbacks to raise it when the page is > + * handed out again. > + */ > +static inline bool pagemap_resets_refcount(const struct dev_pagemap *pgmap) > +{ > + /* > + * MEMORY_DEVICE_GENERIC pages regain a refcount of 1 in the free > + * path. The remaining ZONE_DEVICE types start from 0 here and raise > + * the count again when the allocator or driver hands the page out. > + */ > + switch (pgmap->type) { > + case MEMORY_DEVICE_FS_DAX: > + case MEMORY_DEVICE_PRIVATE: > + case MEMORY_DEVICE_COHERENT: > + case MEMORY_DEVICE_PCI_P2PDMA: > + return false; > + case MEMORY_DEVICE_GENERIC: > + return true; > + default: > + WARN_ONCE(1, "Unknown memory type!"); > + return true; Wouldn't the compiler warn if we would define a new type but forgot to update it here? We're using an enum, and I thought the compiler would bail out in that case. Or are we scared of some other garbage ending up in there? Apart from that LGTM. -- Cheers, David