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b=MCYxIBI/yFb2t84oZWB0/nnRfrtEPFazz6f4DcCv4JizTYM+yTnHZ75/Y19G3YTiWkW9QHLSoqlqss+lPzxTaX4WgAtMQDuXm4HPdFtfI/SsmfWCVNJJraQXUUeoisDW6RE3m7SNP2jLZ8wa8iHz2JRBnh6vtUZ1dfkVsLIUN04= Received: from 30.74.144.127(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WyqQrzH_1770629815 cluster:ay36) by smtp.aliyun-inc.com; Mon, 09 Feb 2026 17:36:56 +0800 Message-ID: <280ae63e-d66e-438f-8045-6c870420fe76@linux.alibaba.com> Date: Mon, 9 Feb 2026 17:36:55 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 4/5] arm64: mm: implement the architecture-specific clear_flush_young_ptes() To: "David Hildenbrand (Arm)" , Chris Mason Cc: akpm@linux-foundation.org, catalin.marinas@arm.com, will@kernel.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.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, dev.jain@arm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <9d866a2644051e13a41ef4d6ca3909c6e1f9e229.1766631066.git.baolin.wang@linux.alibaba.com> <20260128114936.72280-1-clm@meta.com> <07d55759-a50a-457a-badd-85697174116f@kernel.org> From: Baolin Wang In-Reply-To: <07d55759-a50a-457a-badd-85697174116f@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: ntxmzqkhgmn39w7b39q5d8mdixnkyrzg X-Rspamd-Queue-Id: 948B94000C X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1770629822-821187 X-HE-Meta: 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 nyQl7qHN 5PyHf5Z6n+JHxaEiwk4p4rIvALvEKIel2qEriKj4ouHLn+od8QjjjxRDFjYL0HcM5dFgSU8TQDuuLoocAz7Mi+grkiOP0/57JiF6Npe0FHR5vFJdwo1DTIY6m1ysk0qy0B4HfOkeO3L9CL8vDtI9lejSU3lWJgSTbOswkeTuy6TbTbNBD5Ztyd0Kfb7QETOZpV02y0GCvp+MFeizqgSb8qEDw2Ws1Mm6N12Pi+q22KvCyx69xk5TV90tNHnBX5XyW1rcRmNkM2y+uSLFDvlIJC4hmf8eb2kGT7TumOBLjCJwoXbbgX4cOyn5BqzA2Kf+Jf0aI03zG6BVUdhc+dGqFwKxU0iL2znz/aNt0ofcdjc4Sb9WvXAVDd1dk6w== 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 2/9/26 5:09 PM, David Hildenbrand (Arm) wrote: > On 1/29/26 02:42, Baolin Wang wrote: >> >> >> On 1/28/26 7:47 PM, Chris Mason wrote: >>> Baolin Wang wrote: >>>> Implement the Arm64 architecture-specific clear_flush_young_ptes() >>>> to enable >>>> batched checking of young flags and TLB flushing, improving >>>> performance during >>>> large folio reclamation. >>>> >>>> Performance testing: >>>> Allocate 10G clean file-backed folios by mmap() in a memory cgroup, >>>> and try to >>>> reclaim 8G file-backed folios via the memory.reclaim interface. I >>>> can observe >>>> 33% performance improvement on my Arm64 32-core server (and 10%+ >>>> improvement >>>> on my X86 machine). Meanwhile, the hotspot folio_check_references() >>>> dropped >>>> from approximately 35% to around 5%. >>> >>> Hi everyone, I ran mm-new through my AI review prompts and this one was >>> flagged.  AI review below: >>> >>>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/ >>>> asm/pgtable.h >>>> --- a/arch/arm64/include/asm/pgtable.h >>>> +++ b/arch/arm64/include/asm/pgtable.h >>>> @@ -1838,6 +1838,17 @@ static inline int >>>> ptep_clear_flush_young(struct vm_area_struct *vma, >>>>       return contpte_clear_flush_young_ptes(vma, addr, ptep, 1); >>>>   } >>>> >>>> +#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 && !pte_cont(__ptep_get(ptep)))) >>>> +        return __ptep_clear_flush_young(vma, addr, ptep); >>> >>> Should this be checking !pte_valid_cont() instead of !pte_cont()? >>> >>> The existing ptep_clear_flush_young() above uses !pte_valid_cont() to >>> determine when to take the fast path. The new function only checks >>> !pte_cont(), which differs when handling non-present PTEs. >>> >>> Non-present PTEs (device-private, device-exclusive) can reach >>> clear_flush_young_ptes() through folio_referenced_one()-> >>> clear_flush_young_ptes_notify(). These entries may have bit 52 set as >>> part of their encoding, but they aren't valid contiguous mappings. >>> >>> With the current check, wouldn't such entries incorrectly trigger the >>> contpte path and potentially cause contpte_clear_flush_young_ptes() to >>> process additional unrelated PTEs beyond the intended single entry? >> >> Indeed. I previously discussed with Ryan whether using pte_cont() was >> enough, and we believed that invalid PTEs wouldn’t have the PTE_CONT >> bit set. But we clearly missed the device-folio cases. Thanks for >> reporting. >> >> Andrew, could you please squash the following fix into this patch? If >> you prefer a new version, please let me know. Thanks. > > Isn't the real problem that we should never ever ever ever, try clearing > the young bit on a non-present pte? > > See damon_ptep_mkold() how that is handled with the flushing/notify. > > There needs to be a pte_present() check in the caller. The handling of ZONE_DEVICE memory in check_pte() makes me me doubt my earlier understanding. And I think you are right. } else if (pte_present(ptent)) { pfn = pte_pfn(ptent); } else { const softleaf_t entry = softleaf_from_pte(ptent); /* Handle un-addressable ZONE_DEVICE memory */ if (!softleaf_is_device_private(entry) && !softleaf_is_device_exclusive(entry)) return false; pfn = softleaf_to_pfn(entry); } > BUT > > I recall that folio_referenced() should never apply to ZONE_DEVICE > folios. folio_referenced() is only called from memory reclaim code, and > ZONE_DEVICE pages never get reclaimed through vmscan.c Thanks for clarifying. So I can drop the pte valid check.