Received-SPF: pass (google.com: domain of linux-ext4-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <db23875c-750e-d81d-5184-3d53814eebd4@amd.com>
Date:   Wed, 22 Jun 2022 18:06:10 -0500
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
 Thunderbird/91.9.1
Subject: Re: [PATCH v5 01/13] mm: add zone device coherent type memory support
Content-Language: en-US
To:     Alistair Popple <apopple@nvidia.com>,
        David Hildenbrand <david@redhat.com>
Cc:     Felix Kuehling <felix.kuehling@amd.com>, jgg@nvidia.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, willy@infradead.org,
        akpm@linux-foundation.org
References: <20220531200041.24904-1-alex.sierra@amd.com>
 <20220531200041.24904-2-alex.sierra@amd.com>
 <3ac89358-2ce0-7d0d-8b9c-8b0e5cc48945@redhat.com>
 <02ed2cb7-3ad3-8ffc-6032-04ae1853e234@amd.com>
 <7605beee-0a76-4ee9-e950-17419630f2cf@redhat.com>
 <ddcebcc1-fb0a-e565-f14d-77c9d48f2928@amd.com>
 <6aef4b7f-0ced-08cd-1f0c-50c22996aa41@redhat.com>
 <65987ab8-426d-e533-0295-069312b4f751@amd.com>
 <34e94bdb-675a-5d5c-6137-8aa1ee658d49@redhat.com>
 <87letq6wb5.fsf@nvdebian.thelocal>
 <643c44e7-48be-375b-c7ab-6a30b5ee2937@redhat.com>
 <f5b9f777-85a2-9c38-17f3-0c9be1eeb867@amd.com>
 <01cf9f24-d7fc-61e9-1c28-85dc5aabe645@redhat.com>
 <87h74d7dde.fsf@nvdebian.thelocal>
From:   "Sierra Guiza, Alejandro (Alex)" <alex.sierra@amd.com>
In-Reply-To: <87h74d7dde.fsf@nvdebian.thelocal>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?R1RNcXJBazVGdGIvQ0lBb0IrWmhxcjdQaVA4cFU1cHpobGdSajRDa1J3T1M1?=
 =?utf-8?B?TmVqeGtNZGM5eXBXNjBuVStVTUtsOHlQZ0hwNE9ZTXhSTzd1dkFMRDhvMity?=
 =?utf-8?B?RnBheldUNzZFQjl4bXBIVTBDSFFJVjJEdzVkTm1VcStzdGV5Nkw4RFdka3Ft?=
 =?utf-8?B?Sm9vZmtGMFdWYVBJSHZUY2daR0VzSVpUOVI0MkVVaDhLeFBhaS9VWk8xRWdP?=
 =?utf-8?B?b0hCQkR1TCtOMUE4M2NlZUo0TTk0R1FpQUlUaDFFbll2aUhhL2x6UW5hU1V3?=
 =?utf-8?B?Mk1QNHE0cCt5aEQvSG9LcmJlZ0tyb0RKMHQ4bWwvcnJyY1B3ZGtDSS82bjc5?=
 =?utf-8?B?Z0d2QUhBQ3E2L0hzeTIzL0VsaDE5NEI3NkF5aTNRd2dRenVHU1hTSEM5OFI4?=
 =?utf-8?B?Q01XR2VHem5zbEtGMitaOHJPc0gvMzI2UmRaczk2Z3NqVnMra2pWd3RUNm5w?=
 =?utf-8?B?VGx6QmREOG1SSzYrOTM3OHpWb0lid3U2OEhuTWZ6MG5nTFc3N1FGdmt0MURZ?=
 =?utf-8?B?bU40ZEZmWEE0RExaOUtzdVBHVURMazFKdzI3TGxSZTFjVnRJQjVJb0FHaHhn?=
 =?utf-8?B?SDJNZUNDUFRzbko5WWszZ1dqL1JPRHpwTXlHUHVTc1UvdnFzRFZ0Z0FISVhQ?=
 =?utf-8?B?OFpIeWEzakhDL0FxOWJIZEhiRlQxcEdtTFZVTTBWUngyUUxjK29YV2FYN1po?=
 =?utf-8?B?RTNybEdhZjNhMmdBa2JGa2twYzMySkNFYW9MdGxqMjkxWm94UjhkUTBkaDZW?=
 =?utf-8?B?ZXd2QXRyeHVqN3RYRTVwV0RUL1JROE1naGU5QmlpbXFqRzExZ3lhd2t1TmF0?=
 =?utf-8?B?YXhvcGV1UWgyVDRsQUV3MEJRZlFROVRyK1phTTlVQ0FjUHg1VFlnaUphbjZn?=
 =?utf-8?B?WnY2RjFHL0wxelJUZkw4Z3llRFpkQThIMFo3RC94RGtrMzE5OVJZdmtHaHU0?=
 =?utf-8?B?MEdVb1NCKzJ4OUNMK2liaDJ1ckR4M3Q2a1lwZE91VXUreEZXYjVrcHJBZHA5?=
 =?utf-8?B?aVhrMXhLVWFOR2g4ZVM4cmllRlQ5bjRYY05FaXNvKzUxblFTTGZpT0xhTXV6?=
 =?utf-8?B?QlFkVy9Nc09mQ1FlOVJLSXhtSnVHRE9wekVCOFA4SmlZdm44MVJMblVJOW9K?=
 =?utf-8?B?cmxvUFV0YmNxaEgwQ2dwSzVqNWZZbnFNNXFiRUFvN0NVUmxKYit4cWNjUFl2?=
 =?utf-8?B?bmIxdHRNMi9qL1Bwazc2QWZRWHdiejhMMGxnN2E2K3lWRFNHejhadHcwQ1A2?=
 =?utf-8?B?ek8rWjA1VUVpVGJORkxSb2JMd2RKOHdLY0xhV0tMM1daKytCaDhLQy9MUnlI?=
 =?utf-8?B?dmFMY1FOZWF6VkVtTEl4THhUeWJuRFRpTmtjYm5PZUpPU2ZGelpCQzBKQnpN?=
 =?utf-8?B?VW1zNUZXRy9ZejRSWHdoK0tIZDcvZ0o4eVNYcXl1c2k3TWd3enZOb2w4NjJG?=
 =?utf-8?B?TjVrN0pCUkhuRW1vN0VWTVJlcFA4YVZsQkZCM1JDWUIwUk5VWmhsTVR3bVNU?=
 =?utf-8?B?OHczSWRKNkpvZEtMMWE2Q3FHOUlHQVBJMzhvYVBFWHVJN212V3NkcEQvbEVo?=
 =?utf-8?B?K2diSXpQSndwYVM0cWg5NGRnK2prWHFMT1lPQVNBMDRQNGVwaXpHOW8rcG9I?=
 =?utf-8?B?OU0va1F5MVFmZlJUWjVwRkJpYWlKQkthMzVFaEpad0FxRHhmNWlnN0xMNmhF?=
 =?utf-8?B?L3lERkJ2VGd0cGpueTVlZ1lNa3VJNzcxaUNEUk5FMWt6Lzc4d05SbVFyRVd1?=
 =?utf-8?B?em9DUnk3SksvaHFkU3hLQzMyVWNnVUR3Y01OVzliRm54dStqVnFHT3hVSjRR?=
 =?utf-8?B?YXBXN3BadHhBcHEyQnVVczFST3Z3ZDRvUlhnTjc0cFpVVEhLa3IwOWFTd1Zy?=
 =?utf-8?B?Z2p6VTB2K2g0Q3ZrR2hDQXFkOG5uaTdDYUlyQ0RRdGVsT0MzSHE1V0Q5VThQ?=
 =?utf-8?B?UzdpMURjZmN0VlhYTW81VDZlV2R0WjRJQk5DbXNja1k2OW9wUmw1VjBkL3Fp?=
 =?utf-8?B?YTV3ZzcxbTBIb1QzYStLTGEwZjk2bnYvWjVkY1hDdzVMc3pkNVNObTcxQkZv?=
 =?utf-8?B?am90bHlrSXk3anIyMU5VOWo2M3JsMXJlL0VvQStJemNXcGhmSVJVRFhndits?=
 =?utf-8?B?VjF2b2MrWWd0UVFodU81Vlo0aFRxS2E2Y1o0TW9JVzRMVTI0VmRNekxrTndt?=
 =?utf-8?B?dlJSdnBPRlRILzM0UlMweE1CZUhpUDNBMS80R0wxeVhZZnYxNDJjbVdqOHpV?=
 =?utf-8?B?NW1zOVZhRkUxNko3b2FaTFZJZ2tCYysraitZMkJYdWV2QnUyZkdQY3Qwb1Za?=
 =?utf-8?B?UFBVQ1ozU3lsczRTVzQ5ZjRkMkQydHdzeGFvaDNCdzZpMUhzU1VhQT09?=
X-OriginatorOrg: amd.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 06e59371-5028-4a85-4ddb-08da54a3ce88
X-MS-Exchange-CrossTenant-AuthSource: SN6PR12MB2717.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Jun 2022 23:06:14.9819
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: CXyPYlrriKJZMig1L+GaVCKBpQ6VDLAJfzmfweLMBxu64T7yaJlT7TGNcttmIpZWymZnx9G9kmI4t+JYcc/8LA==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB3328
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,
        RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_PASS,T_SCC_BODY_TEXT_LINE
        autolearn=ham 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


On 6/21/2022 7:16 PM, Alistair Popple wrote:
> David Hildenbrand <david@redhat.com> writes:
>
>> On 21.06.22 18:08, Sierra Guiza, Alejandro (Alex) wrote:
>>> On 6/21/2022 7:25 AM, David Hildenbrand wrote:
>>>> On 21.06.22 13:55, Alistair Popple wrote:
>>>>> David Hildenbrand<david@redhat.com>  writes:
>>>>>
>>>>>> On 21.06.22 13:25, Felix Kuehling wrote:
>>>>>>> Am 6/17/22 um 23:19 schrieb David Hildenbrand:
>>>>>>>> On 17.06.22 21:27, Sierra Guiza, Alejandro (Alex) wrote:
>>>>>>>>> On 6/17/2022 12:33 PM, David Hildenbrand wrote:
>>>>>>>>>> On 17.06.22 19:20, Sierra Guiza, Alejandro (Alex) wrote:
>>>>>>>>>>> On 6/17/2022 4:40 AM, David Hildenbrand wrote:
>>>>>>>>>>>> On 31.05.22 22:00, Alex Sierra wrote:
>>>>>>>>>>>>> Device memory that is cache coherent from device and CPU point of view.
>>>>>>>>>>>>> This is used on platforms that have an advanced system bus (like CAPI
>>>>>>>>>>>>> or CXL). Any page of a process can be migrated to such memory. However,
>>>>>>>>>>>>> no one should be allowed to pin such memory so that it can always be
>>>>>>>>>>>>> evicted.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Signed-off-by: Alex Sierra<alex.sierra@amd.com>
>>>>>>>>>>>>> Acked-by: Felix Kuehling<Felix.Kuehling@amd.com>
>>>>>>>>>>>>> Reviewed-by: Alistair Popple<apopple@nvidia.com>
>>>>>>>>>>>>> [hch: rebased ontop of the refcount changes,
>>>>>>>>>>>>>            removed is_dev_private_or_coherent_page]
>>>>>>>>>>>>> Signed-off-by: Christoph Hellwig<hch@lst.de>
>>>>>>>>>>>>> ---
>>>>>>>>>>>>>       include/linux/memremap.h | 19 +++++++++++++++++++
>>>>>>>>>>>>>       mm/memcontrol.c          |  7 ++++---
>>>>>>>>>>>>>       mm/memory-failure.c      |  8 ++++++--
>>>>>>>>>>>>>       mm/memremap.c            | 10 ++++++++++
>>>>>>>>>>>>>       mm/migrate_device.c      | 16 +++++++---------
>>>>>>>>>>>>>       mm/rmap.c                |  5 +++--
>>>>>>>>>>>>>       6 files changed, 49 insertions(+), 16 deletions(-)
>>>>>>>>>>>>>
>>>>>>>>>>>>> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
>>>>>>>>>>>>> index 8af304f6b504..9f752ebed613 100644
>>>>>>>>>>>>> --- a/include/linux/memremap.h
>>>>>>>>>>>>> +++ b/include/linux/memremap.h
>>>>>>>>>>>>> @@ -41,6 +41,13 @@ struct vmem_altmap {
>>>>>>>>>>>>>        * A more complete discussion of unaddressable memory may be found in
>>>>>>>>>>>>>        * include/linux/hmm.h and Documentation/vm/hmm.rst.
>>>>>>>>>>>>>        *
>>>>>>>>>>>>> + * MEMORY_DEVICE_COHERENT:
>>>>>>>>>>>>> + * Device memory that is cache coherent from device and CPU point of view. This
>>>>>>>>>>>>> + * is used on platforms that have an advanced system bus (like CAPI or CXL). A
>>>>>>>>>>>>> + * driver can hotplug the device memory using ZONE_DEVICE and with that memory
>>>>>>>>>>>>> + * type. Any page of a process can be migrated to such memory. However no one
>>>>>>>>>>>> Any page might not be right, I'm pretty sure. ... just thinking about special pages
>>>>>>>>>>>> like vdso, shared zeropage, ... pinned pages ...
>>>>>>>>>> Well, you cannot migrate long term pages, that's what I meant :)
>>>>>>>>>>
>>>>>>>>>>>>> + * should be allowed to pin such memory so that it can always be evicted.
>>>>>>>>>>>>> + *
>>>>>>>>>>>>>        * MEMORY_DEVICE_FS_DAX:
>>>>>>>>>>>>>        * Host memory that has similar access semantics as System RAM i.e. DMA
>>>>>>>>>>>>>        * coherent and supports page pinning. In support of coordinating page
>>>>>>>>>>>>> @@ -61,6 +68,7 @@ struct vmem_altmap {
>>>>>>>>>>>>>       enum memory_type {
>>>>>>>>>>>>>       	/* 0 is reserved to catch uninitialized type fields */
>>>>>>>>>>>>>       	MEMORY_DEVICE_PRIVATE = 1,
>>>>>>>>>>>>> +	MEMORY_DEVICE_COHERENT,
>>>>>>>>>>>>>       	MEMORY_DEVICE_FS_DAX,
>>>>>>>>>>>>>       	MEMORY_DEVICE_GENERIC,
>>>>>>>>>>>>>       	MEMORY_DEVICE_PCI_P2PDMA,
>>>>>>>>>>>>> @@ -143,6 +151,17 @@ static inline bool folio_is_device_private(const struct folio *folio)
>>>>>>>>>>>> In general, this LGTM, and it should be correct with PageAnonExclusive I think.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> However, where exactly is pinning forbidden?
>>>>>>>>>>> Long-term pinning is forbidden since it would interfere with the device
>>>>>>>>>>> memory manager owning the
>>>>>>>>>>> device-coherent pages (e.g. evictions in TTM). However, normal pinning
>>>>>>>>>>> is allowed on this device type.
>>>>>>>>>> I don't see updates to folio_is_pinnable() in this patch.
>>>>>>>>> Device coherent type pages should return true here, as they are pinnable
>>>>>>>>> pages.
>>>>>>>> That function is only called for long-term pinnings in try_grab_folio().
>>>>>>>>
>>>>>>>>>> So wouldn't try_grab_folio() simply pin these pages? What am I missing?
>>>>>>>>> As far as I understand this return NULL for long term pin pages.
>>>>>>>>> Otherwise they get refcount incremented.
>>>>>>>> I don't follow.
>>>>>>>>
>>>>>>>> You're saying
>>>>>>>>
>>>>>>>> a) folio_is_pinnable() returns true for device coherent pages
>>>>>>>>
>>>>>>>> and that
>>>>>>>>
>>>>>>>> b) device coherent pages don't get long-term pinned
>>>>>>>>
>>>>>>>>
>>>>>>>> Yet, the code says
>>>>>>>>
>>>>>>>> struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags)
>>>>>>>> {
>>>>>>>> 	if (flags & FOLL_GET)
>>>>>>>> 		return try_get_folio(page, refs);
>>>>>>>> 	else if (flags & FOLL_PIN) {
>>>>>>>> 		struct folio *folio;
>>>>>>>>
>>>>>>>> 		/*
>>>>>>>> 		 * Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a
>>>>>>>> 		 * right zone, so fail and let the caller fall back to the slow
>>>>>>>> 		 * path.
>>>>>>>> 		 */
>>>>>>>> 		if (unlikely((flags & FOLL_LONGTERM) &&
>>>>>>>> 			     !is_pinnable_page(page)))
>>>>>>>> 			return NULL;
>>>>>>>> 		...
>>>>>>>> 		return folio;
>>>>>>>> 	}
>>>>>>>> }
>>>>>>>>
>>>>>>>>
>>>>>>>> What prevents these pages from getting long-term pinned as stated in this patch?
>>>>>>> Long-term pinning is handled by __gup_longterm_locked, which migrates
>>>>>>> pages returned by __get_user_pages_locked that cannot be long-term
>>>>>>> pinned. try_grab_folio is OK to grab the pages. Anything that can't be
>>>>>>> long-term pinned will be migrated afterwards, and
>>>>>>> __get_user_pages_locked will be retried. The migration of
>>>>>>> DEVICE_COHERENT pages was implemented by Alistair in patch 5/13
>>>>>>> ("mm/gup: migrate device coherent pages when pinning instead of failing").
>>>>>> Thanks.
>>>>>>
>>>>>> __gup_longterm_locked()->check_and_migrate_movable_pages()
>>>>>>
>>>>>> Which checks folio_is_pinnable() and doesn't do anything if set.
>>>>>>
>>>>>> Sorry to be dense here, but I don't see how what's stated in this patch
>>>>>> works without adjusting folio_is_pinnable().
>>>>> Ugh, I think you might be right about try_grab_folio().
>>>>>
>>>>> We didn't update folio_is_pinnable() to include device coherent pages
>>>>> because device coherent pages are pinnable. It is really just
>>>>> FOLL_LONGTERM that we want to prevent here.
>>>>>
>>>>> For normal PUP that is done by my change in
>>>>> check_and_migrate_movable_pages() which migrates pages being pinned with
>>>>> FOLL_LONGTERM. But I think I incorrectly assumed we would take the
>>>>> pte_devmap() path in gup_pte_range(), which we don't for coherent pages.
>>>>> So I think the check in try_grab_folio() needs to be:
>>>> I think I said it already (and I might be wrong without reading the
>>>> code), but folio_is_pinnable() is *only* called for long-term pinnings.
>>>>
>>>> It should actually be called folio_is_longterm_pinnable().
>>>>
>>>> That's where that check should go, no?
>>> David, I think you're right. We didn't catch this since the LONGTERM gup
>>> test we added to hmm-test only calls to pin_user_pages. Apparently
>>> try_grab_folio is called only from fast callers (ex.
>>> pin_user_pages_fast/get_user_pages_fast). I have added a conditional
>>> similar to what Alistair has proposed to return null on LONGTERM &&
>>> (coherent_pages || folio_is_pinnable) at try_grab_folio. Also a new gup
>>> test was added with LONGTERM set that calls pin_user_pages_fast.
>>> Returning null under this condition it does causes the migration from
>>> dev to system memory.
>>>
>> Why can't coherent memory simply put its checks into
>> folio_is_pinnable()? I don't get it why we have to do things differently
>> here.
> I'd made the reasonable assumption that
> folio_is_pinnable()/is_pinnable_page() were used to check if the
> folio/page is pinnable or not regardless of FOLL_LONGTERM. Looking at
> the code more closely though I see both are actually only used on paths
> checking for FOLL_LONGTERM pinning.
>
> So I agree - we should rename these
> folio_is_longterm_pinnable()/is_longterm_pinnable_page() and add the
> check for coherent pages there. Thanks for pointing that out.
>
>   - Alistair

Will do in the next patch series.

Regards,
Alex Sierra

>>> Actually, Im having different problems with a call to PageAnonExclusive
>>> from try_to_migrate_one during page fault from a HMM test that first
>>> migrate pages to device private and forks to mark as COW these pages.
>>> Apparently is catching the first BUG VM_BUG_ON_PGFLAGS(!PageAnon(page),
>>> page)
>> With or without this series? A backtrace would be great.