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Fri, 19 Dec 2025 08:56:11 +0800 Message-ID: <121c8ffb-adff-4766-aae9-8be6d37d546a@linux.alibaba.com> Date: Fri, 19 Dec 2025 08:56:09 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] mm: rmap: support batched checks of the references for large folios To: Ryan Roberts , akpm@linux-foundation.org, david@kernel.org, catalin.marinas@arm.com, will@kernel.org Cc: lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, willy@infradead.org, baohua@kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <545dba5e899634bc6c8ca782417d16fef3bd049f.1765439381.git.baolin.wang@linux.alibaba.com> <89cdd927-fc88-42cf-b8a1-2fbd736d5f7c@linux.alibaba.com> <0caffb55-f242-4b01-b60a-c8749aadf661@arm.com> From: Baolin Wang In-Reply-To: <0caffb55-f242-4b01-b60a-c8749aadf661@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: i6tzgy14hyb9f4rawgr3z5ss7tewymyo X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 73487100003 X-Rspam-User: X-HE-Tag: 1766105776-37586 X-HE-Meta: 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 bPBqbFcd aoeldnc+Zv8ZNq+0ekwur4QzE0oviX4WIW+pNVrqCEQ/pHIU/w0hrOojfMMUEAdqwUzfkaavuGBo3sHcmDZqdcATZKApbuplEYndz+mUg8KECI0mNWZVuGY+i8R0lMFRWPvl8elkleHQQgJDlX1luB+6E7Fi5P9G6WKrAVzbPuu1QnH5t+iS7pvISxUEQgudyys9j9GQ6kxvSg3O0Qnzbn7+4J+6sS1HrbaaNAPKuShFbbQYehZ7JM6FuQhKuKe8c5sxNTAhIZKR5Z/2nw2iYb7LL3SqfNMD6JzCgLZxkhXmDNOA= 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: On 2025/12/18 20:08, Ryan Roberts wrote: >>>>   +#define clear_flush_young_ptes clear_flush_young_ptes >>>> +static inline int clear_flush_young_ptes(struct vm_area_struct *vma, >>>> +                    unsigned long addr, pte_t *ptep, >>>> +                    unsigned int nr) >>>> +{ >>>> +    if (likely(nr == 1)) >>>> +        return __ptep_clear_flush_young(vma, addr, ptep); >>> >>> Bug: This is broken if core-mm tries to call this for nr=1 on a pte that is part >>> of a contpte mapping. >>> >>> The similar fastpaths are here to prevent regressing the common small folio case. >> >> Thanks for catching this. I had considered this before, but I still missed it. >> >>> I guess here the best approach is (note no leading underscores): >>> >>>     if (likely(nr == 1)) >>>         return ptep_clear_flush_young(vma, addr, ptep); >> >> However, I prefer to use pte_cont() to check it. Later, I plan to clean up the >> ptep_clear_flush_young(). >> >>     if (nr == 1 && !pte_cont(__ptep_get(ptep)) >>         return __ptep_clear_flush_young(vma, addr, ptep); > > Sure. That would follow the pattern in clear_young_dirty_ptes(). Please use the > likely() hint as is done everywhere else: > > if (likely(nr == 1 && !pte_cont(__ptep_get(ptep)))) Sure. > I notice that ptep_test_and_clear_young() and ptep_clear_flush_young() are both > testing aginst pte_valid_cont(). These could probably be relaxed to pte_cont() > since it is implicit the the pte must be valid? Yes, I think so. I can do a cleanup later in a separate patch.