Re: [PATCH 1/8] migrate_pages: organize stats with struct migrate_pages_stats

Huang, Ying
2023-01-05T07:07:55Z

Alistair Popple <apopple@nvidia.com> writes:

> "Huang, Ying" <ying.huang@intel.com> writes:
>
>> Alistair Popple <apopple@nvidia.com> writes:
>>
>>> Huang Ying <ying.huang@intel.com> writes:
>>>
>>>> Define struct migrate_pages_stats to organize the various statistics
>>>> in migrate_pages(). This makes it easier to collect and consume the
>>>> statistics in multiple functions. This will be needed in the
>>>> following patches in the series.
>>>>
>>>> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
>>>> Cc: Zi Yan <ziy@nvidia.com>
>>>> Cc: Yang Shi <shy828301@gmail.com>
>>>> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
>>>> Cc: Oscar Salvador <osalvador@suse.de>
>>>> Cc: Matthew Wilcox <willy@infradead.org>
>>>> Cc: Bharata B Rao <bharata@amd.com>
>>>> Cc: Alistair Popple <apopple@nvidia.com>
>>>> Cc: haoxin <xhao@linux.alibaba.com>
>>>> ---
>>>> mm/migrate.c | 58 +++++++++++++++++++++++++++++-----------------------
>>>> 1 file changed, 32 insertions(+), 26 deletions(-)
>>>>
>>>> diff --git a/mm/migrate.c b/mm/migrate.c
>>>> index a4d3fc65085f..ec9263a33d38 100644
>>>> --- a/mm/migrate.c
>>>> +++ b/mm/migrate.c
>>>> @@ -1396,6 +1396,14 @@ static inline int try_split_folio(struct folio *folio, struct list_head *split_f
>>>> return rc;
>>>> }
>>>>
>>>> +struct migrate_pages_stats {
>>>> + int nr_succeeded;
>>>> + int nr_failed_pages;
>>>> + int nr_thp_succeeded;
>>>> + int nr_thp_failed;
>>>> + int nr_thp_split;
>>>
>>> I think some brief comments in the code for what each stat is tracking
>>> and their relationship to each other would be helpful (ie. does
>>> nr_succeeded include thp subpages, etc). Or at least a reference to
>>> where this is documented (ie. page_migration.rst) as I recall there has
>>> been some confusion in the past that has lead to bugs.
>>
>> OK, will do that in the next version.
>
> You should add that nr_failed_pages doesn't count failures of migrations
> that weren't attempted because eg. allocation failure as that was a
> surprising detail to me at least. Unless of course you decide to fix
> that :-)

nr_failed_pages are used for /proc/vmstat. Syscall move_pages() cares
about how many pages requested but not tried. But the system wide
statistics doesn't care about it. I think that is the appropriate.

Best Regards,
Huang, Ying

>>> Otherwise the patch looks good so:
>>>
>>> Reviewed-by: Alistair Popple <apopple@nvidia.com>
>>
>> Thanks!
>>
>> Best Regards,
>> Huang, Ying
>>
>>>> +};
>>>> +
>>>> /*
>>>> * migrate_pages - migrate the folios specified in a list, to the free folios
>>>> * supplied as the target for the page migration
>>>> @@ -1430,13 +1438,8 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>> int large_retry = 1;
>>>> int thp_retry = 1;
>>>> int nr_failed = 0;
>>>> - int nr_failed_pages = 0;
>>>> int nr_retry_pages = 0;
>>>> - int nr_succeeded = 0;
>>>> - int nr_thp_succeeded = 0;
>>>> int nr_large_failed = 0;
>>>> - int nr_thp_failed = 0;
>>>> - int nr_thp_split = 0;
>>>> int pass = 0;
>>>> bool is_large = false;
>>>> bool is_thp = false;
>>>> @@ -1446,9 +1449,11 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>> LIST_HEAD(split_folios);
>>>> bool nosplit = (reason == MR_NUMA_MISPLACED);
>>>> bool no_split_folio_counting = false;
>>>> + struct migrate_pages_stats stats;
>>>>
>>>> trace_mm_migrate_pages_start(mode, reason);
>>>>
>>>> + memset(&stats, 0, sizeof(stats));
>>>> split_folio_migration:
>>>> for (pass = 0; pass < 10 && (retry || large_retry); pass++) {
>>>> retry = 0;
>>>> @@ -1502,9 +1507,9 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>> /* Large folio migration is unsupported */
>>>> if (is_large) {
>>>> nr_large_failed++;
>>>> - nr_thp_failed += is_thp;
>>>> + stats.nr_thp_failed += is_thp;
>>>> if (!try_split_folio(folio, &split_folios)) {
>>>> - nr_thp_split += is_thp;
>>>> + stats.nr_thp_split += is_thp;
>>>> break;
>>>> }
>>>> /* Hugetlb migration is unsupported */
>>>> @@ -1512,7 +1517,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>> nr_failed++;
>>>> }
>>>>
>>>> - nr_failed_pages += nr_pages;
>>>> + stats.nr_failed_pages += nr_pages;
>>>> list_move_tail(&folio->lru, &ret_folios);
>>>> break;
>>>> case -ENOMEM:
>>>> @@ -1522,13 +1527,13 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>> */
>>>> if (is_large) {
>>>> nr_large_failed++;
>>>> - nr_thp_failed += is_thp;
>>>> + stats.nr_thp_failed += is_thp;
>>>> /* Large folio NUMA faulting doesn't split to retry. */
>>>> if (!nosplit) {
>>>> int ret = try_split_folio(folio, &split_folios);
>>>>
>>>> if (!ret) {
>>>> - nr_thp_split += is_thp;
>>>> + stats.nr_thp_split += is_thp;
>>>> break;
>>>> } else if (reason == MR_LONGTERM_PIN &&
>>>> ret == -EAGAIN) {
>>>> @@ -1546,7 +1551,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>> nr_failed++;
>>>> }
>>>>
>>>> - nr_failed_pages += nr_pages + nr_retry_pages;
>>>> + stats.nr_failed_pages += nr_pages + nr_retry_pages;
>>>> /*
>>>> * There might be some split folios of fail-to-migrate large
>>>> * folios left in split_folios list. Move them back to migration
>>>> @@ -1556,7 +1561,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>> list_splice_init(&split_folios, from);
>>>> /* nr_failed isn't updated for not used */
>>>> nr_large_failed += large_retry;
>>>> - nr_thp_failed += thp_retry;
>>>> + stats.nr_thp_failed += thp_retry;
>>>> goto out;
>>>> case -EAGAIN:
>>>> if (is_large) {
>>>> @@ -1568,8 +1573,8 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>> nr_retry_pages += nr_pages;
>>>> break;
>>>> case MIGRATEPAGE_SUCCESS:
>>>> - nr_succeeded += nr_pages;
>>>> - nr_thp_succeeded += is_thp;
>>>> + stats.nr_succeeded += nr_pages;
>>>> + stats.nr_thp_succeeded += is_thp;
>>>> break;
>>>> default:
>>>> /*
>>>> @@ -1580,20 +1585,20 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>> */
>>>> if (is_large) {
>>>> nr_large_failed++;
>>>> - nr_thp_failed += is_thp;
>>>> + stats.nr_thp_failed += is_thp;
>>>> } else if (!no_split_folio_counting) {
>>>> nr_failed++;
>>>> }
>>>>
>>>> - nr_failed_pages += nr_pages;
>>>> + stats.nr_failed_pages += nr_pages;
>>>> break;
>>>> }
>>>> }
>>>> }
>>>> nr_failed += retry;
>>>> nr_large_failed += large_retry;
>>>> - nr_thp_failed += thp_retry;
>>>> - nr_failed_pages += nr_retry_pages;
>>>> + stats.nr_thp_failed += thp_retry;
>>>> + stats.nr_failed_pages += nr_retry_pages;
>>>> /*
>>>> * Try to migrate split folios of fail-to-migrate large folios, no
>>>> * nr_failed counting in this round, since all split folios of a
>>>> @@ -1626,16 +1631,17 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>> if (list_empty(from))
>>>> rc = 0;
>>>>
>>>> - count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
>>>> - count_vm_events(PGMIGRATE_FAIL, nr_failed_pages);
>>>> - 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);
>>>> - trace_mm_migrate_pages(nr_succeeded, nr_failed_pages, nr_thp_succeeded,
>>>> - nr_thp_failed, nr_thp_split, mode, reason);
>>>> + count_vm_events(PGMIGRATE_SUCCESS, stats.nr_succeeded);
>>>> + count_vm_events(PGMIGRATE_FAIL, stats.nr_failed_pages);
>>>> + count_vm_events(THP_MIGRATION_SUCCESS, stats.nr_thp_succeeded);
>>>> + count_vm_events(THP_MIGRATION_FAIL, stats.nr_thp_failed);
>>>> + count_vm_events(THP_MIGRATION_SPLIT, stats.nr_thp_split);
>>>> + trace_mm_migrate_pages(stats.nr_succeeded, stats.nr_failed_pages,
>>>> + stats.nr_thp_succeeded, stats.nr_thp_failed,
>>>> + stats.nr_thp_split, mode, reason);
>>>>
>>>> if (ret_succeeded)
>>>> - *ret_succeeded = nr_succeeded;
>>>> + *ret_succeeded = stats.nr_succeeded;
>>>>
>>>> return rc;
>>>> }