Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
References: <20221216192012.13562-1-mike.kravetz@oracle.com>
 <Y6A6KqXObGKxvDrX@dhcp22.suse.cz> <Y6C6B08nTWusK3RI@monkey>
User-agent: mu4e 1.8.10; emacs 28.2
From:   Alistair Popple <apopple@nvidia.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Michal Hocko <mhocko@suse.com>,
        =?utf-8?B?SsOpcsO0bWU=?= Glisse <jglisse@redhat.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
        linux-s390@vger.kernel.org, netdev@vger.kernel.org,
        David Hildenbrand <david@redhat.com>,
        Peter Xu <peterx@redhat.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Rik van Riel <riel@surriel.com>,
        Will Deacon <will@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Christian Brauner <brauner@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH] mm: remove zap_page_range and change callers to use
 zap_vma_page_range
Date:   Thu, 05 Jan 2023 12:14:36 +1100
In-reply-to: <Y6C6B08nTWusK3RI@monkey>
Message-ID: <87bkndvks7.fsf@nvidia.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?YU5kRWdZWVhpdm45WTc0TldldmRiYlhnb3ZTK1JXTVdsWEZCQWk4K0ZEWE1L?=
 =?utf-8?B?d0xpeDJvSWV4TUFDbFMvS1d4ZFdIUkoxdnpiYkJ0NUxqaHdlb1gwQUpKRXFM?=
 =?utf-8?B?UjN6OC9MZ0RETWplUGNQOU4zR2RlazM1akFvRUd6UHpRUlJYMkpzZVpMamxt?=
 =?utf-8?B?WnVzRURIYmxmcnVWRlc3aG5YTzVhSmNFblpjeE5wUkh1ZVFHQmhHZ2JiUHZH?=
 =?utf-8?B?VlBpR0ttc3BTU0k2L00xM2RoV3VlWlVDVXFMeGlFZm51SjFZWWdQeVZVTko5?=
 =?utf-8?B?aTlOVHBYc3NnZjdCTllSU3M5amo0amk0VkJyRldqeEVqMnZ1akpyVnRzSXFR?=
 =?utf-8?B?d3ljUXVBMWhtbzRmTDRJUy9lR2JzYkwvM2htZXdla0NCRHpEYWVGVGlvOUR3?=
 =?utf-8?B?amliS0cyYTVzSjNLYjFwUnhHQ1BNdWNyVnZTcEg3OCtHeHBwNVVmNlVzRXdK?=
 =?utf-8?B?VEkzTmlveHZSTmE2QzdPNzdGd1VJMEw0enZmZCtEZGoyV1FDRnFGZk5ZLzJN?=
 =?utf-8?B?b1ppL1NHeXJjdWFHSHUyNXArbXd4Q1h5U09BdE5MSk1Ka3dvbzcwU2MwVE5v?=
 =?utf-8?B?eCt3ZWFHWCtzRDRmK084RGdhWk5Jb20xNmhmcjdJRDk3MmdqUkpuVGVlYk9V?=
 =?utf-8?B?MHJxTzBZWDh5OW5zSnJFUkQrZnNXbEhWeWphakxsZEJ5RXUrV2QyRG1GUkNY?=
 =?utf-8?B?SmFGMXRhUndScS80RW15YmlmUHpEVW1tZThBVUNoVFJjSlZQcGVMNzJvSGtr?=
 =?utf-8?B?b0tucVNVczhvbHVrR1F1NTVPY1dxVGhCdzExd3g0SnJKVDJsVGJqa1FtR0h5?=
 =?utf-8?B?cnd4WW56OE4zcjVVK09JQ3lFd1AxN01sdlhFU2N1eEVwSnZBdW1TOFZJbm5n?=
 =?utf-8?B?UXp6RC81MkN6dzkveDFCbWhDbDdnYUtmWENXYTl0SlIvbFZJZ0NhdDNKMlor?=
 =?utf-8?B?KzZ0dnZSVFpOSC9IUkR0MnNFZ05qK21jd2t3aVpBTkFLKzhXQ0tOS2JZNE96?=
 =?utf-8?B?ams2N1ZPZmNJZ3ZGQjlRajkrVDF1dEg1RjV3ZjRQQ21QSlIrYyt2QzRMUUhu?=
 =?utf-8?B?ekJjRmFvYkNhSk5yZml2Tk1Oa3RiT1pPN0svRTVSSkdPWC9PK09DeDhjVncz?=
 =?utf-8?B?YVp3ZThmdk1EMzZPK29ZdlRzZmY0S0ViSDlHbG5NZnBCem1CZUxHeDQ2WGZT?=
 =?utf-8?B?bmlldHNzeDNJUkExL0pteDdMdWJvU1EzbE8xVzlqS2NVa2o1ZjJRRkplajA3?=
 =?utf-8?B?NnJFbXRxM3dBR0FGTlNTOGI1Vld0KzNKZkdaM3dTbkdUUld0cWNpU012NnBV?=
 =?utf-8?B?VEhVSitlODhWcWlaODd6NVVvWSt5M1o1Q2wxZnd3ODY1L0pZY243cDhFd2FV?=
 =?utf-8?B?MTlZUzIyK2QxRkNnTEExT1JiWlI2WjR1RUhjSWJNN29wdFFEVHVtQW9HZzdV?=
 =?utf-8?B?OHIyejdGRzIvWmYvL2ZQM3h6RlRReXU0V0p2VHZ5QmlWaTZZdHg3YkxYekVh?=
 =?utf-8?B?Ung5Y0VGZnpZWXZPQXg3aVV1alNwOUFpeFptYXVYRU5EMnhNVGNKY09sTERZ?=
 =?utf-8?B?V0dnYnpIUCtEUjJNR0U5WUowczlqYUxRenBQL0puOWFjQk4zWEpiZmNZUjlQ?=
 =?utf-8?B?ODFIK05qQnVOL3d5Vmc4eUsxb1BSb3pYQzlodFhQME9PK0FDeloxekpDYkJ3?=
 =?utf-8?B?ZmNtcnpTTVhmSlVQTlVYWnlEV2FaTkNGNjY2V2F3ZHJsb2cvUkYyQndaanUw?=
 =?utf-8?B?NmJyMnFTRW9jaFQvbklsVmVLK2JrSTZOY2VldEE5d1hsZWQxUzVISmYzYTNH?=
 =?utf-8?B?KzgzYmVMaTRxWVBuanNBOFgzSXh2Z3BEZlFua3JUYWoxMmd6Q003OXZJUVNi?=
 =?utf-8?B?ZGNMV3NwTlNSU0xnNHVMTzh5VUlpalRxY3hrNFdxRFU5czRzZUtKV090ZWR4?=
 =?utf-8?B?Y1FKRDFwYXN3Ymo5UnYxOFJ6aHFUeUVkU0pscmZ5SzdoTzBDd0kvOFhHbVRu?=
 =?utf-8?B?VXl2OGhMQ1pkRnFPK0VlL1pGY3orOVg2UTBML2J6WlN1WktwZDZ0YXcwTVBZ?=
 =?utf-8?B?NncwSVRibkVPeWRnSXIrMUF4MFViWVJQNXY5MDFnWHFPQ3B3N2JETVlSaVgw?=
 =?utf-8?Q?GtsSAXoANVX8ukXZZUdVakW7p?=
X-OriginatorOrg: Nvidia.com
X-MS-Exchange-CrossTenant-Network-Message-Id: feb7a98e-c59a-4bff-9c3f-08daeebb23d0
X-MS-Exchange-CrossTenant-AuthSource: BYAPR12MB3176.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Jan 2023 01:21:15.5702
 (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: NfPiGGIpTyBRdhKV3uOxQH9Lh9YyGg4y7iW9/NtRgYvCEBj/BzI7e4XNwy3Sdig+7DcWtUCaEXeLb+mFwxjZ5g==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL0PR12MB4913
X-Spam-Status: No, score=-1.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,
        RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE
        autolearn=no autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


Mike Kravetz <mike.kravetz@oracle.com> writes:

> On 12/19/22 13:06, Michal Hocko wrote:
>> On Fri 16-12-22 11:20:12, Mike Kravetz wrote:
>> > zap_page_range was originally designed to unmap pages within an addres=
s
>> > range that could span multiple vmas.  While working on [1], it was
>> > discovered that all callers of zap_page_range pass a range entirely wi=
thin
>> > a single vma.  In addition, the mmu notification call within zap_page
>> > range does not correctly handle ranges that span multiple vmas as call=
s
>> > should be vma specific.
>>=20
>> Could you spend a sentence or two explaining what is wrong here?
>
> Hmmmm?  My assumption was that the range passed to mmu_notifier_range_ini=
t()
> was supposed to be within the specified vma.  When looking into the notif=
ier
> routines, I could not find any documentation about the usage of the vma w=
ithin
> the mmu_notifier_range structure.  It was introduced with commit bf198b2b=
34bf
> "mm/mmu_notifier: pass down vma and reasons why mmu notifier is happening=
".
> However, I do not see this being used today.
>
> Of course, I could be missing something, so adding J=C3=A9r=C3=B4me.

The only use for mmu_notifier_range->vma I can find is in
mmu_notifier_range_update_to_read_only() which was introduced in
c6d23413f81b ("mm/mmu_notifier: mmu_notifier_range_update_to_read_only()
helper"). However there are no users of that symbol so I think we can
remove it along with the mmu_notifier_range->vma field.

I will put togeather a patch to do that.

>>=20
>> > Instead of fixing zap_page_range, change all callers to use the new
>> > routine zap_vma_page_range.  zap_vma_page_range is just a wrapper arou=
nd
>> > zap_page_range_single passing in NULL zap details.  The name is also
>> > more in line with other exported routines that operate within a vma.
>> > We can then remove zap_page_range.
>>=20
>> I would stick with zap_page_range_single rather than adding a new
>> wrapper but nothing really critical.
>
> I am fine with doing that as well.  My only reason for the wrapper is tha=
t all=20
> callers outside mm/memory.c would pass in NULL zap details.
>
>>=20
>> > Also, change madvise_dontneed_single_vma to use this new routine.
>> >=20
>> > [1] https://lore.kernel.org/linux-mm/20221114235507.294320-2-mike.krav=
etz@oracle.com/
>> > Suggested-by: Peter Xu <peterx@redhat.com>
>> > Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
>>=20
>> Other than that LGTM
>> Acked-by: Michal Hocko <mhocko@suse.com>
>>=20
>> Thanks!
>
> Thanks for taking a look.