Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Zi Yan <ziy@nvidia.com>
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
CC:     <linux-fsdevel@vger.kernel.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>,
        Mike Kravetz <mike.kravetz@oracle.com>
Subject: Re: [PATCH v3 01/25] mm: Introduce struct folio
Date:   Mon, 1 Mar 2021 15:26:11 -0500
Message-ID: <68723D50-AFD1-4F25-8F10-81EC11045BE5@nvidia.com>
In-Reply-To: <20210128070404.1922318-2-willy@infradead.org>
References: <20210128070404.1922318-1-willy@infradead.org>
 <20210128070404.1922318-2-willy@infradead.org>
Content-Type: multipart/signed;
        boundary="=_MailMate_35B182F9-D59B-4424-93FE-9E511CE5CE30_=";
        micalg=pgp-sha512; protocol="application/pgp-signature"
MIME-Version: 1.0
X-MS-Exchange-MessageSentRepresentingType: 1
Received: from [10.2.62.13] (216.228.112.22) by BL1PR13CA0053.namprd13.prod.outlook.com (2603:10b6:208:257::28) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3912.9 via Frontend Transport; Mon, 1 Mar 2021 20:26:14 +0000
X-MS-PublicTrafficType: Email
X-MS-Office365-Filtering-Correlation-Id: 9f3c13e6-c3e5-4272-de89-08d8dcf043db
X-MS-TrafficTypeDiagnostic: MN2PR12MB4285:
X-MS-Exchange-MinimumUrlDomainAge: kernel.org#8760
X-MS-Exchange-Transport-Forked: True
X-Microsoft-Antispam-PRVS: <MN2PR12MB4285EAAC25B1F132D00DCCF8C29A9@MN2PR12MB4285.namprd12.prod.outlook.com>
X-Header: ProcessedBy-CMR-outbound
X-MS-Oob-TLC-OOBClassifiers: OLM:6790;
X-MS-Exchange-SenderADCheck: 1
X-Microsoft-Antispam: BCL:0;
X-Microsoft-Antispam-Message-Info: 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
X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:MN2PR12MB3823.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(4636009)(366004)(376002)(39860400002)(346002)(396003)(136003)(235185007)(83380400001)(5660300002)(4326008)(26005)(36756003)(316002)(16576012)(2906002)(33964004)(33656002)(66946007)(66556008)(66476007)(53546011)(86362001)(8676002)(478600001)(6666004)(8936002)(6486002)(2616005)(956004)(966005)(186003)(16526019)(6916009)(45980500001)(72826003);DIR:OUT;SFP:1101;
X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?cWdJbkJ4UjBCWm1oa0VLeEN1NFRmZ3piTEtuTDdTcmY4ZnZCbDI2Zkc4U1VZ?=
 =?utf-8?B?YStYb2xrY3BLS215V1pjTktEcldhZmMwQXdBUVBTMWY5UTVDYys0TG43d2V1?=
 =?utf-8?B?c3ZCQ1FSK1l0WFAzT1pwVjJjek1EM1ZLb0VtYjFJVDlmeml2QS92TnZIZ2VH?=
 =?utf-8?B?ZEtVa0N4UnB1UVV3NEcxdG5pVWsvZTFCbmErR0RoNXJLUXZ4Nm5JeW1qMFFB?=
 =?utf-8?B?WXhJVzRrSnRaenArS2NuQ3JDbWpvelZrQ0M2R21DQlhCZ1hLVFVBREFQNkhQ?=
 =?utf-8?B?UUlwYlpRQ2xRS3dzU01zaGo4WjYzQ2hWaVJVeGp0MjhvS2FqTkJjMENURU1k?=
 =?utf-8?B?cmZnV1lNSW9BTkNpWUtqZ01IejdZS2JSTDl6VXoyRVpEME9BV3R4eXc0QUNN?=
 =?utf-8?B?S09BQjFCUmV3MVBHcWFjZ0J5aDZ0UXJCYys3QmY0c3ZOUmZXUkNFbE5IakYx?=
 =?utf-8?B?VHJ1emFEWis3bnpNOE1sTW9vWXhadkVZQ2x2MWhKU2hnMWsyMTZFaXhTTm0r?=
 =?utf-8?B?Z3p3c25KanJhUWwzQjgzSTNGSVAxWWR3Si9CQm9DdnlMRXBCZEdMSzBWVW1U?=
 =?utf-8?B?UXZEWE5WcWFvV2U3NVVFdi9VZjJ6VEZ0andwTEZ6SUtpam1xSllzQisybUtv?=
 =?utf-8?B?RXpNRVFlK1lMNm5yMFg5ZTZHVE1UQjVRZXV0QlVRT2h0Y1FKL1k5MDQ1TUU2?=
 =?utf-8?B?VVExSU1SMW84YjQ0aVZYbVpvWDFOWDFFOW9vTG9pYkZTRXpUTTMyR0tjWEpU?=
 =?utf-8?B?NzFkTDNtK0ZoUlpxNFlaL0kzaTJKalBaMGFzSFRTNitFMFRVNkJ1YUFNdmVZ?=
 =?utf-8?B?R2lISnpRby9mRExHUzQ4eGwyU3ZRSlRienYxeDQ4Y0pWS0F6QU1MOUZPc2Vh?=
 =?utf-8?B?UDV1NHZTNjZzZDdwVk11ZEJEdWNycE1YNUFSOGc5dkJBWnF1RWtnc2U1QzEy?=
 =?utf-8?B?ejdSOU9aMzlwYkpaVCtkbjl3NkYrK3g1THpxems1MkloVHlVSkswZ21LRDZF?=
 =?utf-8?B?VlFXRklwbStFT042UHFuZHpTSjU5d1lJcWIvTU42N3MrUUFFNzY1UTNYWUxK?=
 =?utf-8?B?eXdramQ3MFFBVHgyYkR2WENVNTgzdjAzZjZkeWVGMjJTWnJHZ2tNSG9QVnVh?=
 =?utf-8?B?WjZtZlEvUHpuNytwTTFURzVhTXBTdG1FUzBCQzd0aFczYktXL05CWG85NE83?=
 =?utf-8?B?TTNLNC8xZlU5RUVoQ0czMi9MVW9qQUZoNzdPNmZpMVF3K1hVMzB5Tm5vMnhz?=
 =?utf-8?B?YTZNUGxaaFVFcmQ3cG9xZWQ5K3VraHJnL1p5QmNUK2F0ZFpJT25uYWczUkxG?=
 =?utf-8?B?d1pTVityOXA1VDR2c291eHR1NDhOcDN6bkxDYjFwc1dTMHBCU05LbTMwOXFT?=
 =?utf-8?B?NFZjSXQzdTJtUGk0Zm1HRXFvTDZmNFQrdGhyT0RPL08zRldhS3BXM3dkc1Y1?=
 =?utf-8?B?M0ZieTZqZFloRVFkM0FRU3gza3Z2blFsNGdMSFQ5ZFZXTG4xSjJxTTlMaTdL?=
 =?utf-8?B?d1lrWXpnaENqWEtPd2x6MnU5eWplVXFMcFZoZitOS1A3dGhIQ1NUMlJpRkEy?=
 =?utf-8?B?N1BldGE4eFkxZDRxSll5eklOeFdwU3M2ZkdVakQ0RTl2QWdrMWNnbmI1OTZR?=
 =?utf-8?B?UExIQkhnN0FVRGFJcXlSRGhhcVN6OC8vdEJNd3AwWUJrblF6Vm5sM3FzbnhP?=
 =?utf-8?B?TkhwSE95cWtiTVBtNldlcmtLVWgxMkc5cUY3ellhKzJlTkxiL1N3MmxraXQz?=
 =?utf-8?Q?kyB/3wc4GAqU/uQwIRtRlxDxztdRq1H+sJVYLc0?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 9f3c13e6-c3e5-4272-de89-08d8dcf043db
X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB3823.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Mar 2021 20:26:17.2683
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: eMVqs6VJmNTLqdNsHOTL23OOYVq+Vzk/p+pYW8q+kPulCEfNgyZfaJDixlDSFwoJ
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB4285
X-OriginatorOrg: Nvidia.com
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1;
        t=1614630916; bh=TcXNkwWtPCEi561wawVkFCbNQlEdLaajqKxpzBscl1Y=;
        h=ARC-Seal:ARC-Message-Signature:ARC-Authentication-Results:
         Authentication-Results:From:To:CC:Subject:Date:X-Mailer:Message-ID:
         In-Reply-To:References:Content-Type:X-Originating-IP:
         X-ClientProxiedBy:MIME-Version:
         X-MS-Exchange-MessageSentRepresentingType:X-MS-PublicTrafficType:
         X-MS-Office365-Filtering-Correlation-Id:X-MS-TrafficTypeDiagnostic:
         X-MS-Exchange-MinimumUrlDomainAge:X-MS-Exchange-Transport-Forked:
         X-Microsoft-Antispam-PRVS:X-Header:X-MS-Oob-TLC-OOBClassifiers:
         X-MS-Exchange-SenderADCheck:X-Microsoft-Antispam:
         X-Microsoft-Antispam-Message-Info:X-Forefront-Antispam-Report:
         X-MS-Exchange-AntiSpam-MessageData:
         X-MS-Exchange-CrossTenant-Network-Message-Id:
         X-MS-Exchange-CrossTenant-AuthSource:
         X-MS-Exchange-CrossTenant-AuthAs:
         X-MS-Exchange-CrossTenant-OriginalArrivalTime:
         X-MS-Exchange-CrossTenant-FromEntityHeader:
         X-MS-Exchange-CrossTenant-Id:X-MS-Exchange-CrossTenant-MailboxType:
         X-MS-Exchange-CrossTenant-UserPrincipalName:
         X-MS-Exchange-Transport-CrossTenantHeadersStamped:X-OriginatorOrg;
        b=kaOEQDzrJfZRaxadeZCNoSytJSrS1r3iUzh6pafBNn4nCjtcIe5cKLAfPjkBSqmQj
         06gmUkmJbRXDxVLvhCgv9BJY2Gi3pXE8gJM8ZOqlYhrjiIv3bNk88P2YSjGm2TGgS+
         P3Yu4Figqn582dWLyobVOLcqaYnS1CLIoEV7KSf7kGdvAq9t5D9epv6FCSm93VY7Vl
         3sF2endYI1/YfAONmwxU1bgHee0++u2YSe7khdebAeQ33SWTj4DfDCr0r/c8Yxajki
         lNomKGiltjY94c1ycZl4Q/0DG1DZkuERX10wcCRoKQnE4Q5k3fL8AY6o8/sIZA04i1
         PF3nAFCRyl+Lw==
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

--=_MailMate_35B182F9-D59B-4424-93FE-9E511CE5CE30_=
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On 28 Jan 2021, at 2:03, Matthew Wilcox (Oracle) wrote:

> We have trouble keeping track of whether we've already called
> compound_head() to ensure we're not operating on a tail page.  Further,=

> it's never clear whether we intend a struct page to refer to PAGE_SIZE
> bytes or page_size(compound_head(page)).
>
> Introduce a new type 'struct folio' that always refers to an entire
> (possibly compound) page, and points to the head page (or base page).
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  include/linux/mm.h       | 26 ++++++++++++++++++++++++++
>  include/linux/mm_types.h | 17 +++++++++++++++++
>  2 files changed, 43 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 2d6e715ab8ea..f20504017adf 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -924,6 +924,11 @@ static inline unsigned int compound_order(struct p=
age *page)
>  	return page[1].compound_order;
>  }
>
> +static inline unsigned int folio_order(struct folio *folio)
> +{
> +	return compound_order(&folio->page);
> +}
> +
>  static inline bool hpage_pincount_available(struct page *page)
>  {
>  	/*
> @@ -975,6 +980,26 @@ static inline unsigned int page_shift(struct page =
*page)
>
>  void free_compound_page(struct page *page);
>
> +static inline unsigned long folio_nr_pages(struct folio *folio)
> +{
> +	return compound_nr(&folio->page);
> +}
> +
> +static inline struct folio *next_folio(struct folio *folio)
> +{
> +	return folio + folio_nr_pages(folio);

Are you planning to make hugetlb use folio too?

If yes, this might not work if we have CONFIG_SPARSEMEM && !CONFIG_SPARSE=
MEM_VMEMMAP
with a hugetlb folio > MAX_ORDER, because struct page might not be virtua=
lly contiguous.
See the experiment I did in [1].


[1] https://lore.kernel.org/linux-mm/16F7C58B-4D79-41C5-9B64-A1A1628F4AF2=
@nvidia.com/


=E2=80=94
Best Regards,
Yan Zi

--=_MailMate_35B182F9-D59B-4424-93FE-9E511CE5CE30_=
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename="signature.asc"
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=u8ZM
-----END PGP SIGNATURE-----

--=_MailMate_35B182F9-D59B-4424-93FE-9E511CE5CE30_=--