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 4D272407CDC for ; Tue, 9 Jun 2026 12:55:13 +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=1781009714; cv=none; b=nbDOQBSjmWio4CEpbOnyrvd2RGdnTZepS6LMqdn6L6zLb+pnuW61i4iLwIhaBoCPbN8wqHFP6j9l0RyVTNIbjO7cbYjyJb2ix2YhHyOFSGqZIsFil4qvH30f0Z5jwt3wh47oyEu5Cu8AeEoRFmqHv838CwnML5irD2LsngLmF9U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781009714; c=relaxed/simple; bh=x+OfSClobIC7+s+IVl5mGFhWnc5bYBacZOim03ERk3o=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NIq/yWrxZOFZMBPZZYQAA6zOeQOJz9hzAlk7PScuA1Yw+dELU4Y7p+NS2y4Esa9wqpVY5g+SmwJ/PFOa35W7KYL40MWZm+h+7tL/3mDR632BCepGvtf5ntBnov5ryUdGD6CJO0iFRX63UJdbL3rbC7gnj7IAOjmqFDnOjFAo0JU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Hmcc79SC; 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="Hmcc79SC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8F1B31F00893; Tue, 9 Jun 2026 12:55:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781009712; bh=8GHDf/RVnBCewcZpKZyqB+pri2BC8nwPoR8xvqXHq9k=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Hmcc79SCMgkni+sJcI/8+5HS+mWVebR4K17jduHY+OeIRwe3RK2DsWPisDmo7IwUP ioOp2IvwyIMA9FPmBE5YoQhvULFL7z5bpL4wPfIDMrrs0DVAvrfZCHn+xzYouW6v8U OnQgP13ik5xmMRTLDqGyp7T76KG1QI+w7o3ZAsg54n1pHo8ihKtwCfUq5N6WiYvEZ3 Eq3dFy2qF9ysM3jnm5Dzgg8096y06bJzaODWjkYoIebQgh2D7kpKk1cnHpdUcUN2D1 J5L2VQvvvLeMURZ7t9ugzOi4gr+Hrl54Ri8knQSZE9RvKaFQFY5/T+jqMz3bvk/vBV Q/MaQyh+3bOKg== Message-ID: Date: Tue, 9 Jun 2026 14:55:00 +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 3/7] mm/migrate: skip data copy for already-copied folios To: "Garg, Shivank" , Zi Yan Cc: akpm@linux-foundation.org, kinseyho@google.com, weixugc@google.com, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, willy@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, dave@stgolabs.net, rkodsara@amd.com, vkoul@kernel.org, bharata@amd.com, sj@kernel.org, rientjes@google.com, xuezhengchu@huawei.com, yiannis@zptcorp.com, dave.hansen@intel.com, hannes@cmpxchg.org, jhubbard@nvidia.com, peterx@redhat.com, riel@surriel.com, shakeel.butt@linux.dev, stalexan@redhat.com, tj@kernel.org, nifan.cxl@gmail.com, jic23@kernel.org, aneesh.kumar@kernel.org, nathan.lynch@amd.com, Frank.li@nxp.com, djbw@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260428155043.39251-2-shivankg@amd.com> <20260428155043.39251-8-shivankg@amd.com> <810e9a58-9c08-4f5e-af5f-866685ca09b2@kernel.org> <7e6a7626-5a1b-4672-91bd-85b0f4ee2ecb@amd.com> <7430d69a-616b-40cf-a2e8-6ef4e57b6857@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: 7bit On 6/8/26 21:32, Garg, Shivank wrote: > > > On 6/8/2026 9:13 PM, David Hildenbrand (Arm) wrote: >> On 6/8/26 17:41, Zi Yan wrote: >>> >>> >>> IIRC, multithreaded copy is already gated by CONFIG_HIGHMEM, otherwise >>> it needs to perform kmap_local() at each copying CPU, which complicates >>> the process. Then, this code will only used for 32bit without highmem, >>> I assume there will no page copy DMA on 32bit platform. Maybe it is not >>> too bad to limit this to 64bit. > > I agree. > >> >> I'm more concerned of CONFIG_64BIT handling in the code, but if that can be >> avoided easily, fine with me. > > > MIGRATION_COPY_OFFLOAD will not be enabled for !64BIT at config. > config MIGRATION_COPY_OFFLOAD > bool "Page migration copy offload" > depends on MIGRATION && 64BIT Might we worth documenting somewhere why, like ... > > I think only place in code we need #ifdef is: > enum { > FOLIO_WAS_MAPPED = BIT(0), > FOLIO_WAS_MLOCKED = BIT(1), > FOLIO_OLD_STATES = FOLIO_WAS_MAPPED | FOLIO_WAS_MLOCKED, > #ifdef CONFIG_MIGRATION_COPY_OFFLOAD > FOLIO_CONTENT_COPIED = BIT(2), > #else > FOLIO_CONTENT_COPIED = 0, ... here /* On 32bit we do not have a spare bit, migration-copy offload is disabled. */ > #endif > }; > > With FOLIO_CONTENT_COPIED=0, this will be no operation for its bit operation. > > eg: > const bool already_copied = dst->migrate_info & FOLIO_CONTENT_COPIED; > evaluates 0 for !64BIT. If that does the trick, good! -- Cheers, David