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Thu, 29 Jan 2026 09:42:14 +0800 Message-ID: Date: Thu, 29 Jan 2026 09:42:12 +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: Chris Mason Cc: akpm@linux-foundation.org, david@kernel.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> From: Baolin Wang In-Reply-To: <20260128114936.72280-1-clm@meta.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 3F50440005 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 9p53y47jojkfoy6wduitt4nncjay43n5 X-HE-Tag: 1769650937-120139 X-HE-Meta: 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 TJvD2tRF U4RRNRpDlxTFTO6aroGT4BQaEPmEag50WRZgfiz5iVDgyVhJv4IIeT7UgAxYpCYkfr5coJcz32ZNLv+5ONsNAV5NSsTVFcA10q/SjJ0z8MgYXR/RRRgHupLlN88vEC9fKABOMTBN+llRdiYcz5uN4RjQGh3vjPh5j2aY3Ru1c7AWpITm1fOhaA6ITs6gpVAWGEzMISrkZb22xfCv4PHUYHNA0lOHWm1bZgrGpGsvpKU/Gd8njVo6t+los0XSiF9ULE3w35r4H03ejKUxtT/DBUa+OXktyI94PD7ukfGImKftERJL0/SsIda8VcsFDpR6Qmydzz0sudxJIkyrMyzRtOp26x1J6KtA6d4fqN9Y0QxN/ENZ/99vM0wgKLA== 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 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. diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index a17eb8a76788..dc16591c4241 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -1843,7 +1843,7 @@ 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)))) + if (likely(nr == 1 && !pte_valid_cont(__ptep_get(ptep)))) return __ptep_clear_flush_young(vma, addr, ptep); return contpte_clear_flush_young_ptes(vma, addr, ptep, nr);