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[2003:cb:c702:6e00:8b72:420e:df27:90c2]) by smtp.gmail.com with ESMTPSA id h67-20020a1c2146000000b003d1de805de5sm13076781wmh.16.2022.12.13.06.42.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Dec 2022 06:42:56 -0800 (PST) Message-ID: <6d33b510-e913-5738-1e87-9f70da2ccee0@redhat.com> Date: Tue, 13 Dec 2022 15:42:55 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH -next 1/8] mm: memory_hotplug: add pfn_to_online_folio() To: Kefeng Wang , Andrew Morton , Oscar Salvador , SeongJae Park Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, damon@lists.linux.dev, vishal.moola@gmail.com, willy@infradead.org References: <20221213092735.187924-1-wangkefeng.wang@huawei.com> <20221213092735.187924-2-wangkefeng.wang@huawei.com> <801ccbe2-08b8-e1cb-9aee-614d59a807d2@huawei.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <801ccbe2-08b8-e1cb-9aee-614d59a807d2@huawei.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 7B63D40013 X-Stat-Signature: 9iownp1d4sxq843ab9kt9mbagi99wxd7 X-HE-Tag: 1670942581-476238 X-HE-Meta: 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 lHVhfiKH DgnXH3y3XQfhCOcgSFNHoXxX5EhAkdxwZkhUIj1UxISmn5amrfo+pJbbTtfHnweq+WfnGUZ5VUffsghO+ZqLepRYxmDfWv8cqlzeZvn3w26nO0G+M0e2xEngnpvm8UTsgIFi+3OuJ6gcgwab8McryYagiuVRsbkNiI3aJvZaW+/ZJGSUVT8Oo6tGUbXkXTXGbGnx39XCUFiPEb0ZuYDdhjpEfLH0gtehoyTkcQ//4osEvrItIvXIfhST5keL9PYKSdmmowJ1U/xEHgWE= 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 13.12.22 13:13, Kefeng Wang wrote: > > On 2022/12/13 19:40, David Hildenbrand wrote: >> On 13.12.22 10:27, Kefeng Wang wrote: >>> Introduce a wrapper function pfn_to_online_folio(), which calls >>> pfn_to_online_page() and returns the folio of the page found, >>> or null if no page. >>> >>> Signed-off-by: Kefeng Wang >>> --- >>>   include/linux/memory_hotplug.h | 7 +++++++ >>>   1 file changed, 7 insertions(+) >>> >>> diff --git a/include/linux/memory_hotplug.h >>> b/include/linux/memory_hotplug.h >>> index 9fcbf5706595..e841e4fb52a7 100644 >>> --- a/include/linux/memory_hotplug.h >>> +++ b/include/linux/memory_hotplug.h >>> @@ -265,6 +265,13 @@ static inline void pgdat_kswapd_unlock(pg_data_t >>> *pgdat) {} >>>   static inline void pgdat_kswapd_lock_init(pg_data_t *pgdat) {} >>>   #endif /* ! CONFIG_MEMORY_HOTPLUG */ >>>   +static inline struct folio *pfn_to_online_folio(unsigned long pfn) >>> +{ >>> +    struct page *page = pfn_to_online_page(pfn); >>> + >>> +    return page ? page_folio(page) : NULL; >>> +} >> >> Who guarantees that page_folio() is safe and stable at that point? >> >> IIRC, that's very tricky. We could have the page concurrently getting >> freed and the folio dissolved. > So the caller should consider this,  lock or get the folio in the caller? > I think the helper pfn_to_online_folio() as is might be wrong approach. The caller should convert to a folio after taking precautions that it is actually safe to do that (e.g., succeeded grabbing a reference first). -- Thanks, David / dhildenb