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

Otherwise the patch looks good so:

Reviewed-by: Alistair Popple <apopple@nvidia.com>

> +};
> +
> /*
> * 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;
> }

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