Re: [PATCH V4] mm/vmstat: Add events for THP migration without split

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 07/09/2020 11:12 PM, Zi Yan wrote:
> On 9 Jul 2020, at 12:39, Randy Dunlap wrote:
> 
>> On 7/9/20 9:34 AM, Zi Yan wrote:
>>> On 9 Jul 2020, at 11:34, Randy Dunlap wrote:
>>>
>>>> Hi,
>>>>
>>>> I have a few comments on this.
>>>>
>>>> a. I reported it very early and should have been Cc-ed.
>>>>
>>>> b. A patch that applies to mmotm or linux-next would have been better
>>>> than a full replacement patch.
>>>>
>>>> c. I tried replacing what I believe is the correct/same patch file in mmotm
>>>> and still have build errors.
>>>>
>>>> (more below)
>>>>
>>>> On 7/9/20 2:39 AM, Anshuman Khandual wrote:
>>>>
>>>>> ---
>>>>> Applies on 5.8-rc4.
>>>>>
>>>>> Changes in V4:
>>>>>
>>>>> - Changed THP_MIGRATION_FAILURE as THP_MIGRATION_FAIL per John
>>>>> - Dropped all conditional 'if' blocks in migrate_pages() per Andrew and John
>>>>> - Updated migration events documentation per John
>>>>> - Updated thp_nr_pages variable as nr_subpages for an expected merge conflict
>>>>> - Moved all new THP vmstat events into CONFIG_MIGRATION
>>>>> - Updated Cc list with Documentation/ and tracing related addresses
>>>>>
>>>>> Changes in V3: (https://patchwork.kernel.org/patch/11647237/)
>>>>>
>>>>> - Formatted new events documentation with 'fmt' tool per Matthew
>>>>> - Made events universally available i.e dropped ARCH_ENABLE_THP_MIGRATION
>>>>> - Added THP_MIGRATION_SPLIT
>>>>> - Updated trace_mm_migrate_pages() with THP events
>>>>> - Made THP events update normal page migration events as well
>>>>>
>>>>> Changes in V2: (https://patchwork.kernel.org/patch/11586893/)
>>>>>
>>>>> - Dropped PMD reference both from code and commit message per Matthew
>>>>> - Added documentation and updated the commit message per Daniel
>>>>>
>>>>> Changes in V1: (https://patchwork.kernel.org/patch/11564497/)
>>>>>
>>>>> - Changed function name as thp_pmd_migration_success() per John
>>>>> - Folded in a fix (https://patchwork.kernel.org/patch/11563009/) from Hugh
>>>>>
>>>>> Changes in RFC V2: (https://patchwork.kernel.org/patch/11554861/)
>>>>>
>>>>> - Decopupled and renamed VM events from their implementation per Zi and John
>>>>> - Added THP_PMD_MIGRATION_FAILURE VM event upon allocation failure and split
>>>>>
>>>>> Changes in RFC V1: (https://patchwork.kernel.org/patch/11542055/)
>>>>>
>>>>>  Documentation/vm/page_migration.rst | 27 +++++++++++++++
>>>>>  include/linux/vm_event_item.h       |  3 ++
>>>>>  include/trace/events/migrate.h      | 17 ++++++++--
>>>>>  mm/migrate.c                        | 52 ++++++++++++++++++++++++-----
>>>>>  mm/vmstat.c                         |  3 ++
>>>>>  5 files changed, 91 insertions(+), 11 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
>>>>> index 24fc7c3ae7d6..2e6ca53b9bbd 100644
>>>>> --- a/include/linux/vm_event_item.h
>>>>> +++ b/include/linux/vm_event_item.h
>>>>> @@ -56,6 +56,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>>>>>  #endif
>>>>>  #ifdef CONFIG_MIGRATION
>>>>>  		PGMIGRATE_SUCCESS, PGMIGRATE_FAIL,
>>>>> +		THP_MIGRATION_SUCCESS,
>>>>> +		THP_MIGRATION_FAIL,
>>>>> +		THP_MIGRATION_SPLIT,
>>>> These 3 new symbols are still only present if CONFIG_MIGRATION=y, but the build errors
>>>> are using these symbols even when CONFIG_MIGRATION is not set.
>>>>
>>>>>  #endif
>>>>>  #ifdef CONFIG_COMPACTION
>>>>>  		COMPACTMIGRATE_SCANNED, COMPACTFREE_SCANNED,
>>>>> diff --git a/mm/migrate.c b/mm/migrate.c
>>>>> index f37729673558..c706e3576cfc 100644
>>>>> --- a/mm/migrate.c
>>>>> +++ b/mm/migrate.c
>>>>> @@ -1429,22 +1429,35 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>>>  		enum migrate_mode mode, int reason)
>>>>>  {
>>>>>  	int retry = 1;
>>>>> +	int thp_retry = 1;
>>>>>  	int nr_failed = 0;
>>>>>  	int nr_succeeded = 0;
>>>>> +	int nr_thp_succeeded = 0;
>>>>> +	int nr_thp_failed = 0;
>>>>> +	int nr_thp_split = 0;
>>>>>  	int pass = 0;
>>>>> +	bool is_thp = false;
>>>>>  	struct page *page;
>>>>>  	struct page *page2;
>>>>>  	int swapwrite = current->flags & PF_SWAPWRITE;
>>>>> -	int rc;
>>>>> +	int rc, nr_subpages;
>>>>>
>>>>>  	if (!swapwrite)
>>>>>  		current->flags |= PF_SWAPWRITE;
>>>>>
>>>>> -	for(pass = 0; pass < 10 && retry; pass++) {
>>>>> +	for (pass = 0; pass < 10 && (retry || thp_retry); pass++) {
>>>>>  		retry = 0;
>>>>> +		thp_retry = 0;
>>>>>
>>>>>  		list_for_each_entry_safe(page, page2, from, lru) {
>>>>>  retry:
>>>>> +			/*
>>>>> +			 * THP statistics is based on the source huge page.
>>>>> +			 * Capture required information that might get lost
>>>>> +			 * during migration.
>>>>> +			 */
>>>>> +			is_thp = PageTransHuge(page);
>>>>> +			nr_subpages = hpage_nr_pages(page);
>>>>>  			cond_resched();
>>>>>
>>>>>  			if (PageHuge(page))
>>>>> @@ -1475,15 +1488,30 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>>>  					unlock_page(page);
>>>>>  					if (!rc) {
>>>>>  						list_safe_reset_next(page, page2, lru);
>>>>> +						nr_thp_split++;
>>>>>  						goto retry;
>>>>>  					}
>>>>>  				}
>>>>> +				if (is_thp) {
>>>>> +					nr_thp_failed++;
>>>>> +					nr_failed += nr_subpages;
>>>>> +					goto out;
>>>>> +				}
>>>>>  				nr_failed++;
>>>>>  				goto out;
>>>>>  			case -EAGAIN:
>>>>> +				if (is_thp) {
>>>>> +					thp_retry++;
>>>>> +					break;
>>>>> +				}
>>>>>  				retry++;
>>>>>  				break;
>>>>>  			case MIGRATEPAGE_SUCCESS:
>>>>> +				if (is_thp) {
>>>>> +					nr_thp_succeeded++;
>>>>> +					nr_succeeded += nr_subpages;
>>>>> +					break;
>>>>> +				}
>>>>>  				nr_succeeded++;
>>>>>  				break;
>>>>>  			default:
>>>>> @@ -1493,19 +1521,27 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>>>  				 * removed from migration page list and not
>>>>>  				 * retried in the next outer loop.
>>>>>  				 */
>>>>> +				if (is_thp) {
>>>>> +					nr_thp_failed++;
>>>>> +					nr_failed += nr_subpages;
>>>>> +					break;
>>>>> +				}
>>>>>  				nr_failed++;
>>>>>  				break;
>>>>>  			}
>>>>>  		}
>>>>>  	}
>>>>> -	nr_failed += retry;
>>>>> +	nr_failed += retry + thp_retry;
>>>>> +	nr_thp_failed += thp_retry;
>>>>>  	rc = nr_failed;
>>>>>  out:
>>>>> -	if (nr_succeeded)
>>>>> -		count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
>>>>> -	if (nr_failed)
>>>>> -		count_vm_events(PGMIGRATE_FAIL, nr_failed);
>>>>> -	trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);
>>>>> +	count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
>>>>> +	count_vm_events(PGMIGRATE_FAIL, nr_failed);
>>>>> +	count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);
>>>>> +	count_vm_events(THP_MIGRATION_FAIL, nr_thp_failed);
>>>>> +	count_vm_events(THP_MIGRATION_SPLIT, nr_thp_split);
>>>> These references still cause build errors.
>>>>
>>>>> +	trace_mm_migrate_pages(nr_succeeded, nr_failed, nr_thp_succeeded,
>>>>> +			       nr_thp_failed, nr_thp_split, mode, reason);
>>>>>
>>>>>  	if (!swapwrite)
>>>>>  		current->flags &= ~PF_SWAPWRITE;
>>>>> diff --git a/mm/vmstat.c b/mm/vmstat.c
>>>>> index 3fb23a21f6dd..09914a4bfee4 100644
>>>>> --- a/mm/vmstat.c
>>>>> +++ b/mm/vmstat.c
>>>>> @@ -1234,6 +1234,9 @@ const char * const vmstat_text[] = {
>>>>>  #ifdef CONFIG_MIGRATION
>>>>>  	"pgmigrate_success",
>>>>>  	"pgmigrate_fail",
>>>>> +	"thp_migration_success",
>>>>> +	"thp_migration_fail",
>>>>> +	"thp_migration_split",
>>>>>  #endif
>>>>>  #ifdef CONFIG_COMPACTION
>>>>>  	"compact_migrate_scanned",
>>>>>
>>> Which arch are you building? I did not see any error
>>> after applying this patch on mmotm (reverting the existing ones)
>>> and compiling them on x86_64. I used make x86_64_defconfig and
>>> unselected COMPACTION and MIGRATION.
>> Hi,
>>
>> I am trying to build x86_64.
>> Maybe I am just having trouble replacing the patch file.
>> Like I tried to say, I would prefer to see an incremental patch
>> to fix mmotm or linux-next.
> I agree. The patch does not apply to mmotm. Can you try the incremental
> patch below? It should apply to mmotm.
> 
> 
> Hi Andrew and Anshuman,
> 
> Should Anshuman resend the incremental patch or Andrew can fold it along
> with the two patches in mmotm into one?

V3 patch and fixes on it were reverted from linux-next yesterday. The change
for V4 patch was not small, hence just went with a fresh one instead. Please
do let me know if this is still not settled and needs further action.

https://lore.kernel.org/linux-next/20200709182150.7b49e5e8@canb.auug.org.au/T/#u