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Sat, 07 Mar 2026 09:28:30 +0800 Message-ID: Date: Sat, 7 Mar 2026 09:28:29 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 6/6] arm64: mm: implement the architecture-specific test_and_clear_young_ptes() To: "David Hildenbrand (Arm)" , akpm@linux-foundation.org Cc: 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, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <7f891d42a720cc2e57862f3b79e4f774404f313c.1772778858.git.baolin.wang@linux.alibaba.com> <6305e05e-2911-42b0-b6f5-7fdde787b778@kernel.org> From: Baolin Wang In-Reply-To: <6305e05e-2911-42b0-b6f5-7fdde787b778@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 033DE14000D X-Stat-Signature: zxzpqc5bddppwdt3yuxcm3kuiedx6dim X-Rspam-User: X-HE-Tag: 1772846915-591902 X-HE-Meta: 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 lQcoeRQB dGsXlFdXZ+wwpd8s53PTAY8EaX7o0jYySz8frO4YAtpT9w3AL2ofUPBhyEWBRY48HTdKDrJALPf2wp51jQsuUXCsoPybsddtDwdd9OYR5gFgwM/DvoohoVcg/+GCo6OvTGwPl3sta2lhW5858nh6tsYWWJxsRAlNzvqbUOO+GCzh8GoNwFyK4cWghcPEJ8stE1fHE8N9Hzy5cYuI/jDQ+T1oTcr/RlqpkGP/poDg7qRlBtDg+Ij/g9TLZkQMzJbLBly4ZPCRWRF9zGD8kMzqUp/oYrab1idzgQW19oqLExSumotn8XXoxWWNX3s2SE1Rn9VeENOKBs95+JBUoLlR4vjmt9h9V87DHdls6sqziPVwji1VeplDGJ0vqQYTkfrXKW+gJwQv1JCuXYBgpy6WOjKGSc2nhOXpHnETg/YzUF7hWt70gQ+m/BhVs0w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/6/26 10:47 PM, David Hildenbrand (Arm) wrote: > On 3/6/26 07:43, Baolin Wang wrote: >> Implement the Arm64 architecture-specific test_and_clear_young_ptes() to enable >> batched checking of young flags, improving performance during large folio >> reclamation when MGLRU is enabled. >> >> While we're at it, simplify ptep_test_and_clear_young() by calling >> test_and_clear_young_ptes(). Since callers guarantee that PTEs are present >> before calling these functions, we can use pte_cont() to check the CONT_PTE >> flag instead of pte_valid_cont(). >> >> Performance testing: >> Enable MGLRU, then 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 60%+ performance improvement on my Arm64 32-core server (and about >> 15% improvement on my X86 machine). >> >> W/o patchset: >> real 0m0.470s >> user 0m0.000s >> sys 0m0.470s >> >> W/ patchset: >> real 0m0.180s >> user 0m0.001s >> sys 0m0.179s >> >> Reviewed-by: Rik van Riel >> Signed-off-by: Baolin Wang >> --- >> arch/arm64/include/asm/pgtable.h | 18 ++++++++++++------ >> 1 file changed, 12 insertions(+), 6 deletions(-) >> >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >> index aa4b13da6371..ab451d20e4c5 100644 >> --- a/arch/arm64/include/asm/pgtable.h >> +++ b/arch/arm64/include/asm/pgtable.h >> @@ -1812,16 +1812,22 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm, >> return __ptep_get_and_clear(mm, addr, ptep); >> } >> >> +#define test_and_clear_young_ptes test_and_clear_young_ptes >> +static inline int test_and_clear_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_test_and_clear_young(vma, addr, ptep); >> + >> + return contpte_test_and_clear_young_ptes(vma, addr, ptep, nr); >> +} > > Thinking out loud, what would happen if Good questions, I think the contpte_test_and_clear_young_ptes() takes that into account. > (a) The range spans multiple possible cont ranges (like, 64 ptes). The contpte_test_and_clear_young_ptes() will call contpte_align_addr_ptep() to align the range to cont‑block boundary, that means the range can span multiple cont blocks. int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep, unsigned int nr) { unsigned long end = addr + nr * PAGE_SIZE; int young = 0; ptep = contpte_align_addr_ptep(&addr, &end, ptep, nr); for (; addr != end; ptep++, addr += PAGE_SIZE) young |= __ptep_test_and_clear_young(vma, addr, ptep); return young; } > > (b) The first pte is !pte_cont(), but some others in there are? IMO they can’t be handled in a single batch. Since the folio_pte_batch() will group consecutive !cont PTEs into one batch and consecutive cont PTEs into another (assume all PTEs belong to a single large folio), because their PTE entries have different CONT bits. Even if the callers do so, contpte_align_addr_ptep() will check the pte_cont() of the start and end address to align the range appropriately.