From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CF00939EF3F; Mon, 1 Jun 2026 11:13:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780312441; cv=none; b=bGvNSEySv196b3mBzg0UPIKKY0a8ZsHkN+wMha0pH+NkbftbqO6VAaIiycAI/jB29U9IE48xtfGBuvLAZLQrHTYPJDA6SYJesih/AcwLl2PQklQ+DmIYWJG37mvaQnLPIye3c6L4deN1gjePJfFI7V04omi4jD7PmZcH25MO+aY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780312441; c=relaxed/simple; bh=bQ1Ej8a7BLGgt9b3gLcM0p5S5YPbwbO5Id5o4fXYo2s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rOVvsNXva1aftHZ16bldytU4lKfTxKyKDZELFK+Rc0bWYKitrnxvUH0GzXjLCKAJIzf1K4urYG0KJC6MOiko351+c5FBvRR8sjyDuhpjXoDsgPGbgHvjRlbdik6UorfZWZ9hYrKRdyG4hzkjuted+z2A3exFSzXnC7fveRUXQWI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JI/ED0+I; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JI/ED0+I" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B30A91F00893; Mon, 1 Jun 2026 11:13:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780312439; bh=MU9TAz0HXMedTgLQwpQphoQUdyRWB1XQN6t0YBVfU+c=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=JI/ED0+Ie/4RvUtVTeagEIBW0222r6wWcagxIo5iAb+ATF4U9PqUYo8PhF/kAnH9/ N4J/moLBgYh3DZ9fKmp5qDPXuW+Z14iZrbhXIOaskN9IVCFkZbRp1+mKWkEzO+AAhw PKkoWfULx7CIcCTq9slqn2ZFkqDXVoGrT27O2Ug9OLn65ozq1kN4kbNBsNAt7w8XcT 9FDn77vct2dYjJHQ72b2Vpb5cbCYOakXA4BXJx6xIk48K01RIZz4oQ022/nKCT+/LV EvU89ul2BRBAYsd7opuWp9JfjmF9oIGR6SFoSyMEdaRUUlsgq7EgXz7k6+RpHyU+X5 6Jhe2Kdi/YLUA== Message-ID: <06d9b665-945f-4967-9ed9-b06514478996@kernel.org> Date: Mon, 1 Jun 2026 13:13:40 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v18 06/14] mm/khugepaged: generalize collapse_huge_page for mTHP collapse To: Lance Yang Cc: npache@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, liam@infradead.org, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com, usama.arif@linux.dev References: <2024af56-5e99-4799-a586-e9ba756cecb9@kernel.org> <20260601032804.96122-1-lance.yang@linux.dev> <616de1a8-1cfd-40b8-b04f-7b324be40bfd@linux.dev> <6b11bf0a-769c-4ef2-ac6f-2af38200a6bc@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/1/26 12:47, Lance Yang wrote: > > > On 2026/6/1 18:23, David Hildenbrand (Arm) wrote: >> On 6/1/26 11:08, Lance Yang wrote: >>> >>> >>> >>> One small thing, I think we should probably keep the smp_wmb(), and just >>> move it before the earlier pmd_populate(). >>> >>> IIUC, the ordering we want is still: >>> >>>    clear old PTEs >>>    smp_wmb() >>>    pmd_populate() >>> >>> so another CPU cannot walk through the re-installed PMD and still observe >>> the old PTEs, right? >> >> There is a smp_wmb() in __folio_mark_uptodate(), that should be sufficient? > > Ah, cool! __folio_mark_uptodate() already does the job :P > > So yeah, no extra smp_wmb() needed here! Yeah. BTW, I think we'd need a spin_lock_nested(), so @Nico, treat my code as a draft. -- Cheers, David