Received-SPF: pass (google.com: domain of linux-ext4-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
From:   Alistair Popple <apopple@nvidia.com>
To:     Felix Kuehling <felix.kuehling@amd.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Alex Sierra <alex.sierra@amd.com>, jgg@nvidia.com,
        david@redhat.com, linux-mm@kvack.org, rcampbell@nvidia.com,
        linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        hch@lst.de, jglisse@redhat.com, akpm@linux-foundation.org
Subject: Re: [PATCH v1 1/3] mm: split vm_normal_pages for LRU and non-LRU
 handling
Date:   Thu, 17 Mar 2022 13:50:37 +1100
References: <20220310172633.9151-1-alex.sierra@amd.com>
 <20220310172633.9151-2-alex.sierra@amd.com>
 <YipQqqpTz8hZAbLZ@casper.infradead.org>
 <651099d6-21ae-16a6-e500-a87002468cda@amd.com>
User-agent: mu4e 1.6.9; emacs 27.1
In-reply-to: <651099d6-21ae-16a6-e500-a87002468cda@amd.com>
Message-ID: <87mthp8f2g.fsf@nvdebian.thelocal>
Content-Type: multipart/mixed; boundary="=-=-="
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?TE9ZVGE1bUk2SVpxaUcxQXNBU1o2RUtycG5FMkFXUUpuRDVsQ1hXaXR2TEFQ?=
 =?utf-8?B?eFpaZnRldTFTYjF1MGhGYVE4L2FnaHVpZXNVVFVTSUN5WjUrdkxka2dsTnBi?=
 =?utf-8?B?UEVXOGJ5MkxpRHlmWWNRZ3pTQTBITkJlaGVMeDkvbXQyUzNzZ3dFTjV2bUFO?=
 =?utf-8?B?Q215dTBnODUvN3ZENjNGdWs1U0FiYyt1RzFFTWZra1dGNHF2UTRqbGcyOTI5?=
 =?utf-8?B?bjBZVXNlMXh2L2hLNldDQUMxdzRsa2trWWpZZEpTTzduYTE4RFNKUzRYNitY?=
 =?utf-8?B?ZUtrdWRjWk1TTFJDMS9NT3EvaGVPRXhVcTVNZnUyK2ZUM1RNWDFzMUR1Y1VB?=
 =?utf-8?B?RzhrQ2JxRGJnQ0JnbThuNk41SzJXM2JUN25lU2prWHQvMHJCQXQ3ZUgzYmxE?=
 =?utf-8?B?Tzgxa2hRRHppM0s2L00zVlRxZVlTL1VOVmg2VWQyUlZXVVNMM2I3LzdudVBY?=
 =?utf-8?B?Rm1OUnB5Q2F6bWQ5bUpVcTAxY1E4a2IyKzNic09weW9YY1pBMFd0VFd4THE1?=
 =?utf-8?B?aVFhK2tkeW9aODFjcG1xdVdDcTYxVmtxeCt3WjJjS09COVpxMHVlMEp3eENw?=
 =?utf-8?B?a0FmaytvbkdaWVhCRGk0c215enR5WmhVUDBGSjNvdVhDNWpnTWNDQlQzVU9m?=
 =?utf-8?B?aVlzTWdiWVkrbXhnTU13dGUwVHFxbWZ6SUJjem9VbUpOeDFXYU8vTnZadjI0?=
 =?utf-8?B?Q3hULzNWb080d005NEVaUGROUzlyNnhQYU1lZXMyckpsK2FyYUJ0V1BaT3ha?=
 =?utf-8?B?bjdzZ1BsZStnR1pOaUxmMkFwdSt2SW5aT2Zzek1ucXF0YTUzNkVvZU82dllS?=
 =?utf-8?B?YTRUbW1Odnk3OVZiRUEwYTU4NFBoNzBzMlV1ZUJXWHVIVXlrWDMzL3E4Z1A1?=
 =?utf-8?B?ZXlQQ2JvMUllWk9JU1BOOU1kQUpUVDFCNUZuZGZrT1ByQ2ROcnNoRFJpTWlm?=
 =?utf-8?B?VzlXSVpFLzBreUdpeEh5Y0FPTnAzREVpZDBxZTFkRFhSajIyYkV3YTZ0ek1I?=
 =?utf-8?B?Um1ma1hUeS8xZEpvektLSS9rMmVneGN6UWluc212aEhtbngyamxsR0orb1oz?=
 =?utf-8?B?MFdISVRObExvaXBtNFAzQWhtTTRtR1diVmJ4bVhoMzJyVWhtd2QycVp4QWw5?=
 =?utf-8?B?MTllQ2xudm1LTUVBUTczNXIwbmNmR0VLUlBZb1k2K0ZqTkwyaCt6YlpYWjBz?=
 =?utf-8?B?QktJNlE5eXZxUEZhRCtzWHV2eVd6b2RaTGI1Y01wNHhQZDR3NlhqclZ1bE9w?=
 =?utf-8?B?Zk5BOVJNRmtGcUFrVVRueFlDNThCYkh5RmFYYUNueXJkcUxmYmRhY0xJNXJ5?=
 =?utf-8?B?MnpmL01rUmdUSmJIVEVwT2pDZktmK0FHVnBnT2VsWlNoQ2xQUnVqVWxpdFhH?=
 =?utf-8?B?T1FuL29Wa0IxNXByN3JPS05RV0RMcisyWXVBTXN2SlhlclFjTFhBUDdHNCs4?=
 =?utf-8?B?cmhJSytUZFJaZm9abE05bmJudk5MdExvSk9xRkkzQ1lITmZNWGhmSVZ0OEIv?=
 =?utf-8?B?M285SUhNZ3U2cHRIV2RJQVR4eCtuMzB1Vy9Va2VNcmp5dmsvdTJDZzdNWnRR?=
 =?utf-8?B?T1pvK05hWHVHQTlIdThJYmZDaXQvZFFpTmFoN0FDMHRLQjNzbVNIRVdjUjlP?=
 =?utf-8?B?Y0FDcmZOZ2psc1BFMlRhZlNDbC85eDl4RjFUR280VkYxeUdLRFpGWmI3ZEV0?=
 =?utf-8?B?cEw2R3c5ZVlndmxJbHdDQ2tOVXpEMkRTcmpPY1FaNko2akZQOEdZb05CajNM?=
 =?utf-8?B?WUxELzFnYi9UeGdjTXZuRjQzYVFpMWJHV3gyaHluVXVneXFvbCtzSE4vMlFl?=
 =?utf-8?B?TXF1Y3d1bUVPUllOY3BGOHR2S1V1YkIxYmxENzNTNGN2NzNsdlVuZWpzWnJF?=
 =?utf-8?B?NXJDSktNMUtzdVJGZTkwMFlvQUpEdVluM0RNZTd6Uis5TE9pVUZ4akV6dU1O?=
 =?utf-8?Q?GVhZGIzbrAF7PoSfAuE0luZF7sF4I3PK?=
X-OriginatorOrg: Nvidia.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 19b376ff-c325-4f39-e142-08da07c15b7d
X-MS-Exchange-CrossTenant-AuthSource: BYAPR12MB3176.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Mar 2022 02:53:47.4842
 (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: Njvebd9FEeupqJel0mMFzNMP8IsU4YZjVqaer1R5AOakRYQQAOtR6Hca85D4biXVkdcBfU+4PwCfDetAHcU4Tw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR12MB1607
X-Spam-Status: No, score=-3.5 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
	DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,RDNS_NONE,SPF_HELO_NONE,T_SCC_BODY_TEXT_LINE
	autolearn=unavailable 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-ext4.vger.kernel.org>
X-Mailing-List: linux-ext4@vger.kernel.org

--=-=-=
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

Felix Kuehling <felix.kuehling@amd.com> writes:

> Am 2022-03-10 um 14:25 schrieb Matthew Wilcox:
>> On Thu, Mar 10, 2022 at 11:26:31AM -0600, Alex Sierra wrote:
>>> @@ -606,7 +606,7 @@ static void print_bad_pte(struct vm_area_struct *vm=
a, unsigned long addr,
>>>    * PFNMAP mappings in order to support COWable mappings.
>>>    *
>>>    */
>>> -struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long =
addr,
>>> +struct page *vm_normal_any_page(struct vm_area_struct *vma, unsigned l=
ong addr,
>>>   			    pte_t pte)
>>>   {
>>>   	unsigned long pfn =3D pte_pfn(pte);
>>> @@ -620,8 +620,6 @@ struct page *vm_normal_page(struct vm_area_struct *=
vma, unsigned long addr,
>>>   			return NULL;
>>>   		if (is_zero_pfn(pfn))
>>>   			return NULL;
>>> -		if (pte_devmap(pte))
>>> -			return NULL;
>>>     		print_bad_pte(vma, addr, pte, NULL);
>>>   		return NULL;
>> ... what?
>>
>> Haven't you just made it so that a devmap page always prints a bad PTE
>> message, and then returns NULL anyway?
>
> Yeah, that was stupid. :/=C2=A0 I think the long-term goal was to get rid=
 of
> pte_devmap. But for now, as long as we have pte_special with pte_devmap,
> we'll need a special case to handle that like a normal page.
>
> I only see the PFN_DEV|PFN_MAP flags set in a few places: drivers/dax/dev=
ice.c,
> drivers/nvdimm/pmem.c, fs/fuse/virtio_fs.c. I guess we need to test at le=
ast one
> of them for this patch series to make sure we're not breaking them.
>
>
>>
>> Surely this should be:
>>
>> 		if (pte_devmap(pte))
>> -			return NULL;
>> +			return pfn_to_page(pfn);
>>
>> or maybe
>>
>> +			goto check_pfn;
>>
>> But I don't know about that highest_memmap_pfn check.
>
> Looks to me like it should work. highest_memmap_pfn gets updated in
> memremap_pages -> pagemap_range -> move_pfn_range_to_zone ->
> memmap_init_range.

FWIW the previous version of this feature which was removed in 25b2995a35b6
("mm: remove MEMORY_DEVICE_PUBLIC support") had a similar comparison with
highest_memmap_pfn:

if (likely(pfn <=3D highest_memmap_pfn)) {
        struct page *page =3D pfn_to_page(pfn);

        if (is_device_public_page(page)) {
                if (with_public_device)
                        return page;
                return NULL;
        }
}

> Regards,
> =C2=A0 Felix
>
>
>>
>>> @@ -661,6 +659,22 @@ struct page *vm_normal_page(struct vm_area_struct =
*vma, unsigned long addr,
>>>   	return pfn_to_page(pfn);
>>>   }
>>>   +/*
>>> + * vm_normal_lru_page -- This function gets the "struct page" associat=
ed
>>> + * with a pte only for page cache and anon page. These pages are LRU h=
andled.
>>> + */
>>> +struct page *vm_normal_lru_page(struct vm_area_struct *vma, unsigned l=
ong addr,
>>> +			    pte_t pte)
>> It seems a shame to add a new function without proper kernel-doc.
>>

--=-=-=--