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b=QpaCy0kzVd4IM6z6DErGLY+U81uSuhZNpp97Oy6ER3Mhj0ry4O2rjFJv4YuLDpuJW SLje45zN8tKMCDqQpfecKeqg1BpGsCusv4+O+BgEf1/ZgKfh0Sbu1pA4/5eBbL/N/8 l+QkmCo8KGkZ+s1VlQ15q4HgVxNY+e58LuFLkZX3HweDwVrXiKDN45FNAiospV98w+ oxVzVIskWVUi5Jk16M5x6/YBWOo+HykdpgVafv/ot6GwFHaoSfKJGmc1Bt9wUFDaXI N0pT3nwBvcZDxqNy7E2Ue2yL8p5RdeEd3NfAQ2+kA0D+VJ2tZ+70xb9d5TBoQ/YQkN rGiHwyo/HpxUg== Message-ID: <07d55759-a50a-457a-badd-85697174116f@kernel.org> Date: Mon, 9 Feb 2026 10:09:32 +0100 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: Baolin Wang , 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> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 20CA740010 X-Stat-Signature: mwou8n4jgddsyw8r9hq668d1bkm6ny4a X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1770628181-664055 X-HE-Meta: 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 dcK+o7bP r9ChF/IM4xmRqc4jVzenmHMDq7ZOd/dCc2qXqDeLb0D6yFpItBLdoQyaaMAD5nQMFwdXxGQLWsMysnFk+Tv6aGX+k5cItqcz46QtWu81o9YtAkpw1nWAwmsgMbpPzmY3HjVxpyrQADSk7H62SZKWweCeEb0h4SOS8ZEBnIAsr9QRlN2glJU8Z6ZLmYsyMSzWi7WTLJHo7ISmOE6is6+jWELKJS/UuiJ/YvkfLsIc61N3uKhINn6zEn8AgkZDHxET9S05Nvx413vZiiaG2dm8kGwO+dsJ5E8S7cU/IRkep5Ir949OH6p6rdTFEPbd4ltpD2TpkpJvJkvgkXEvlW39hKDRsyGKVaKAeH3HJ 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 1/29/26 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. 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 -- Cheers, David