Message-ID: <c7c7f5ed-ef80-ef6f-4a73-806b21e7c65d@intel.com>
Date:   Fri, 17 Mar 2023 21:28:57 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101
 Firefox/102.0 Thunderbird/102.8.0
Subject: Re: [PATCH v4 34/36] rmap: add folio_add_file_rmap_range()
To:     Ryan Roberts <ryan.roberts@arm.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        <linux-arch@vger.kernel.org>
CC:     <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
References: <20230315051444.3229621-1-willy@infradead.org>
 <20230315051444.3229621-35-willy@infradead.org>
 <387dc921-de2b-f244-985c-d1e6336d5909@arm.com>
 <01071d9c-483f-2d95-87a6-e1030acaf8dd@arm.com>
 <0f581d0d-3139-4007-2161-592a0a545b50@intel.com>
 <fe743597-cefa-4bf8-aa3f-da9cc10bbd5f@arm.com>
 <f3ffe13c-321a-07f6-6a6f-1a67f585ffe2@intel.com>
 <2b41a6dd-130b-acf3-72fd-b996272c1710@arm.com>
Content-Language: en-US
From:   "Yin, Fengwei" <fengwei.yin@intel.com>
In-Reply-To: <2b41a6dd-130b-acf3-72fd-b996272c1710@arm.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?ZitIZnY5akU2VDNBZm9tRWZKOER1dUo1K1V6aWhYaThFOE9PWkIzN3dmMHNh?=
 =?utf-8?B?RFV3QUw2ZVV3NnN3QVZGV3RWUmk3S3BzWkVCMmJwa1hDR0h3Zmc2NlM4QjNo?=
 =?utf-8?B?a1JUMEcwWkRmQmluK0xQVTVLOVc0UFVyY1B3L1gxVWlLY2FSck9kRkEyN3hS?=
 =?utf-8?B?cngvZllJMTVpWGFSSldoSSs2OGZCVFcyNjVVdkZPRG0yanZDMFJsQW1LSldQ?=
 =?utf-8?B?WW1FZlNoSmw4MjdYZk5uekFlTVZSWmFOUkJPQkFPdWtNYnBDK0FiQUc1UjVr?=
 =?utf-8?B?UUY4YVZlOWxnMUNvL0tKZm9WQnBGbkpMZ2RCMmNVTUpBTTdZN09DQlhqQVV0?=
 =?utf-8?B?cUJSeEFPNGg3QXhZRWx2bUVUTG93c2JJT2szTTFWOTlHSDk1NjhXWFRDYUVx?=
 =?utf-8?B?UVFPUGY3RThiOFNkVS9VMzRXcGswS0J6NXlCeGt1NitzS1JMYktHUHJlNStW?=
 =?utf-8?B?c2pxazV1Rm9RREhqYkpoSjZXM3UwRXVqZG00Q1Jrd21RWGE1UWxXdmtZUDly?=
 =?utf-8?B?eXZzM0k4bW9DVjc1MURlZTdoSU1ZOWQ1UDR2N2R4eG5meTlIa3ErOVBLS3I3?=
 =?utf-8?B?RVhaWE9GY0tFUmtLUExDMHVMTE9KK0YxK1g3a1h2cTBKWmpjalNzRUV5Z2lE?=
 =?utf-8?B?ZU5CbWxJZ3U3TTU5bXNHeEhHMmpTTnM2dHlMVlZJOWh3dXN2NENvei92L05S?=
 =?utf-8?B?WTlxYzFpemtlU3UxQWg5bzdGb3NoaHJaa3lEOUt1dTVlUEJTVlBVQkpEcVFm?=
 =?utf-8?B?U0k0b000bW96QzQ2NlgxSzV4TTVTZWVGbVBoNUZyZDJUVDFMNXIzQ1lEQkVy?=
 =?utf-8?B?Q0xjOUhaNlJpQnl0eGI3ZDBwLzNKSXhweTJ0S1VRVDZ5MExwNWJTMDRua1Bv?=
 =?utf-8?B?UU5rMEo4aFVCT1FvZGc2cUZoanJ6V1Z2Nm5WMEhjNktsMWxEbnMyaXI5Sk0y?=
 =?utf-8?B?M0lQLzRvekVPTWo5OEFDNk1RSTQ4NlUydEk1Y2FwV2paeEx5QWFqa2JDRlpB?=
 =?utf-8?B?ckRxc0tWU2ZDNkZ3VlhhZ2c5V2VPeG80TXVEK3dFS1hQd1NxVmZkZ0VaTk9B?=
 =?utf-8?B?SnFyUENnelBub2dpdmlFR2h3am0zd0RIWmJMUVNjYlZuK1RncTZRTTBKaGlW?=
 =?utf-8?B?cUlSQUFJaHBPeVBKWVpySVVLczZucnB1cndsMEVIZVRZQzJMZXNoeWFsTzND?=
 =?utf-8?B?UUc1UHM4ZENnSjRNZFRTbTlTN0IwOStaaDlRZlVvZldwQ2NLMk5ZT3UxWEp6?=
 =?utf-8?B?SE4zWWJ6aWlSUUVaRGZsa2NodGZidHU1VW5nNHJTZGpQa05URUIwQW9MMEVB?=
 =?utf-8?B?THp5RE5udHUzcVVZUHBHelYweFpkdmJMbzA1VlM5OXc4Z1QvKzFkbGJLZEZS?=
 =?utf-8?B?Tk1FK2lmWi9oT0ViWFVTVjl3MWZKRU5XTGU0WEoxSGM4ellhL0wxbkprdThk?=
 =?utf-8?B?dGt4T09yeFBTWTZad1dPNk5QbTBNdklkVithWEVXN1NYTUM2MEh4dGw4UGNs?=
 =?utf-8?B?cFdLUVhBekxXNkhPZEp1SytRS1UvOWxBZlJwT0RyTFFneVRxVE14anV6L2xk?=
 =?utf-8?B?Qkp1a1BrQUROaENvN080OEhXUzBYLzNrb1dYekZNQjZUWUVHZzdWZlBwMlRX?=
 =?utf-8?B?d1FtOXZNaGZJUHNmK1ZtdURMZ2s1eUtQSlZiUjhGR1ZNc2d0eHNwSGNlN1VB?=
 =?utf-8?B?TU54eGhMR1o5WFFTTkhFQWpsa214OUlPQ3Azb2FDdlg1V2NjT0J6N2dnY0NC?=
 =?utf-8?B?L1FZR3YwZTF2MEdpNk9UOExVbVBnLysvZTd2WFBhNmVXdHNiV3k0Y05LTmww?=
 =?utf-8?B?cmtlcjBpeEhiRG9nalNqaU1aZjFIcnR4bjhrREFNKzlxY3dHNnFXeEtPVm5V?=
 =?utf-8?B?aTI1eWpNb0ZmTm5LN29uN21waE5sYXdXZzJDWUNpSk9IeTRmZ0cxalBqOFZs?=
 =?utf-8?B?ZHNWK1JreHhFSDhqWmRLMjNnZ29KWGpIb3J3VUE3UVBkMGgzNUZVYnd3b0d2?=
 =?utf-8?B?aFd0c1RkTzM0SzRpNnVFRDUwNE1mbndPeTN2MS9SQ3p4d1JaVEFlQUxRaTF1?=
 =?utf-8?B?eEloaFV2UThhcy9LZU9rd3kvWWRiZkpNaVhVRk5wV1pRdU5YUEJ3OHZ1bVJM?=
 =?utf-8?B?NkJJWjlXVm9kL2Q5VzRHQ2tGbXFHemVBNGd1dnZjYVcvckRiWTN0MFAxZThP?=
 =?utf-8?B?TEE9PQ==?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 6896de00-ffe0-4e33-df73-08db26eb951e
X-MS-Exchange-CrossTenant-AuthSource: CO1PR11MB4820.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Mar 2023 13:29:06.5774
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: hMZqXo6AVOBnaVv5vC3hiw6Z/Vv+9VuVZxj0kjEMlarbCaiqkbKNt/O2HlXKWtDM5gIb/r7b6EQlZjo6rY7PZw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR11MB8372
X-OriginatorOrg: intel.com
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 3/17/2023 8:46 PM, Ryan Roberts wrote:
> On 17/03/2023 08:23, Yin, Fengwei wrote:
> [...]
> 
>>>>>> FYI, I'm seeing a perf regression of about 1% when compiling the kernel on
>>>>>> Ampere Altra (arm64) with this whole series on top of v6.3-rc1 (In a VM using
>>>>>> ext4 filesystem). Looks like instruction aborts are taking much longer and a
>>>>>> selection of syscalls are a bit slower. Still hunting down the root cause. Will
>>>>>> report once I have conclusive diagnosis.
>>>>>
>>>>> I'm sorry - I'm struggling to find the exact cause. But its spending over 2x the
>>>>> amount of time in the instruction abort handling code once patches 32-36 are
>>>>> included. Everything in the flame graph is just taking longer. Perhaps we are
>>>>> getting more instruction aborts somehow? I have the flamegraphs if anyone wants
>>>>> them - just shout and I'll email them separately.
>>>> Thanks a lot to Ryan for sharing the flamegraphs to me. I found the __do_fault()
>>>> is called with patch 32-36 while no __do_fault() just with first 31 patches. I 
>>>> suspect the folio_add_file_rmap_range() missed some PTEs population. Please give
>>>> me few days to find the root cause and fix. Sorry for this.
>>>
>>> You're welcome. Give me a shout once you have a re-spin and I'll rerun the tests.
>> Could you please help to try following changes? Thanks in advance.
>>
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index 40be33b5ee46..137011320c68 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -3504,15 +3504,16 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>>  		if (!pte_none(vmf->pte[count]))
>>  			goto skip;
>>  
>> -		if (vmf->address == addr)
>> -			ret = VM_FAULT_NOPAGE;
>> -
>>  		count++;
>>  		continue;
>>  skip:
>>  		if (count) {
>>  			set_pte_range(vmf, folio, page, count, addr);
>>  			folio_ref_add(folio, count);
>> +			if ((vmf->address < (addr + count * PAGE_SIZE)) &&
>> +					(vmf->address >= addr))
>> +				ret = VM_FAULT_NOPAGE;
>> +
>>  		}
>>  
>>  		count++;
>> @@ -3525,6 +3526,9 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>>  	if (count) {
>>  		set_pte_range(vmf, folio, page, count, addr);
>>  		folio_ref_add(folio, count);
>> +		if ((vmf->address < (addr + count * PAGE_SIZE)) &&
>> +				(vmf->address >= addr))
>> +			ret = VM_FAULT_NOPAGE;
>>  	}
>>  
>>  	vmf->pte = old_ptep;
>>
> 
> I'm afraid this hasn't fixed it, and I still see __do_fault(). I'll send the
> flame graph over separately.
> 
> Given I'm running on ext4, I wasn't expecting to see any large page cache
> folios? So I don't think we would have expected this patch to help anyway? (or
> perhaps there are still THP folios? But I think they will get PMD mapped?).
OK. I will try to reproduce the issue on my local env to see whether I could
reproduce it on x86_64 env.


Regards
Yin, Fengwei

> 
> 
>>
>> Regards
>> Yin, Fengwei
>>
>>>
>>>>
>>>>
>>>> Regards
>>>> Yin, Fengwei
>>>>
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Ryan
>>>>>>
>>>>>>
>>>>>>> +			}
>>>>>>> +
>>>>>>> +			if (first)
>>>>>>> +				nr++;
>>>>>>> +		} while (page++, --nr_pages > 0);
>>>>>>>  	} else if (folio_test_pmd_mappable(folio)) {
>>>>>>>  		/* That test is redundant: it's for safety or to optimize out */
>>>>>>>  
>>>>>>> @@ -1354,6 +1362,30 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>>>>>>>  	mlock_vma_folio(folio, vma, compound);
>>>>>>>  }
>>>>>>>  
>>>>>>> +/**
>>>>>>> + * page_add_file_rmap - add pte mapping to a file page
>>>>>>> + * @page:	the page to add the mapping to
>>>>>>> + * @vma:	the vm area in which the mapping is added
>>>>>>> + * @compound:	charge the page as compound or small page
>>>>>>> + *
>>>>>>> + * The caller needs to hold the pte lock.
>>>>>>> + */
>>>>>>> +void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>>>>>>> +		bool compound)
>>>>>>> +{
>>>>>>> +	struct folio *folio = page_folio(page);
>>>>>>> +	unsigned int nr_pages;
>>>>>>> +
>>>>>>> +	VM_WARN_ON_ONCE_PAGE(compound && !PageTransHuge(page), page);
>>>>>>> +
>>>>>>> +	if (likely(!compound))
>>>>>>> +		nr_pages = 1;
>>>>>>> +	else
>>>>>>> +		nr_pages = folio_nr_pages(folio);
>>>>>>> +
>>>>>>> +	folio_add_file_rmap_range(folio, page, nr_pages, vma, compound);
>>>>>>> +}
>>>>>>> +
>>>>>>>  /**
>>>>>>>   * page_remove_rmap - take down pte mapping from a page
>>>>>>>   * @page:	page to remove mapping from
>>>>>>
>>>>>
>>>
>>>
>