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

[Zi Yan <ziy@nvidia.com>]

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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.

mm/migrate.c and added vm events will not be used
if CONFIG_MIGRATION is unchecked. Why would they cause compilation errors?


—
Best Regards,
Yan Zi

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