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Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vpNH5-0000000F61H-0Sxw; Mon, 09 Feb 2026 09:09:43 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vpNH4-0000000F60W-209K for linux-arm-kernel@lists.infradead.org; Mon, 09 Feb 2026 09:09:42 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 8A0DC60008; Mon, 9 Feb 2026 09:09:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D26BBC116C6; Mon, 9 Feb 2026 09:09:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770628181; bh=5nuDSACBfO1w4dYNx+WaobWzgCQZBOlLbjl0OCUaDVg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; 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-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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