Re: [PATCH 1/2] migrate_pages_batch: simplify retrying and failure counting of large folios
From: Alistair Popple
Date: Tue May 09 2023 - 00:34:10 EST
Huang Ying <ying.huang@xxxxxxxxx> writes:
> After recent changes to the retrying and failure counting in
> migrate_pages_batch(), it was found that it's unnecessary to count
> retrying and failure for normal, large, and THP folios separately.
> Because we don't use retrying and failure number of large folios
> directly. So, in this patch, we simplified retrying and failure
> counting of large folios via counting retrying and failure of normal
> and large folios together. This results in the reduced line number.
>
> This is just code cleanup, no functionality changes are expected.
Quite a nice cleanup, thanks. Feel free to add:
Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx>
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Cc: Xin Hao <xhao@xxxxxxxxxxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Cc: Yang Shi <shy828301@xxxxxxxxx>
> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Alistair Popple <apopple@xxxxxxxxxx>
> ---
> mm/migrate.c | 103 +++++++++++++++++----------------------------------
> 1 file changed, 35 insertions(+), 68 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 01cac26a3127..10709aed76d3 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1614,11 +1614,9 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> int nr_pass)
> {
> int retry = 1;
> - int large_retry = 1;
> int thp_retry = 1;
> int nr_failed = 0;
> int nr_retry_pages = 0;
> - int nr_large_failed = 0;
> int pass = 0;
> bool is_large = false;
> bool is_thp = false;
> @@ -1631,9 +1629,8 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> VM_WARN_ON_ONCE(mode != MIGRATE_ASYNC &&
> !list_empty(from) && !list_is_singular(from));
>
> - for (pass = 0; pass < nr_pass && (retry || large_retry); pass++) {
> + for (pass = 0; pass < nr_pass && retry; pass++) {
> retry = 0;
> - large_retry = 0;
> thp_retry = 0;
> nr_retry_pages = 0;
>
> @@ -1660,7 +1657,7 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> * list is processed.
> */
> if (!thp_migration_supported() && is_thp) {
> - nr_large_failed++;
> + nr_failed++;
> stats->nr_thp_failed++;
> if (!try_split_folio(folio, split_folios)) {
> stats->nr_thp_split++;
> @@ -1688,38 +1685,33 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> * When memory is low, don't bother to try to migrate
> * other folios, move unmapped folios, then exit.
> */
> - if (is_large) {
> - nr_large_failed++;
> - 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) {
> - stats->nr_thp_split += is_thp;
> - break;
> - } else if (reason == MR_LONGTERM_PIN &&
> - ret == -EAGAIN) {
> - /*
> - * Try again to split large folio to
> - * mitigate the failure of longterm pinning.
> - */
> - large_retry++;
> - thp_retry += is_thp;
> - nr_retry_pages += nr_pages;
> - /* Undo duplicated failure counting. */
> - nr_large_failed--;
> - stats->nr_thp_failed -= is_thp;
> - break;
> - }
> + nr_failed++;
> + stats->nr_thp_failed += is_thp;
> + /* Large folio NUMA faulting doesn't split to retry. */
> + if (is_large && !nosplit) {
> + int ret = try_split_folio(folio, split_folios);
> +
> + if (!ret) {
> + stats->nr_thp_split += is_thp;
> + break;
> + } else if (reason == MR_LONGTERM_PIN &&
> + ret == -EAGAIN) {
> + /*
> + * Try again to split large folio to
> + * mitigate the failure of longterm pinning.
> + */
> + retry++;
> + thp_retry += is_thp;
> + nr_retry_pages += nr_pages;
> + /* Undo duplicated failure counting. */
> + nr_failed--;
> + stats->nr_thp_failed -= is_thp;
> + break;
> }
> - } else {
> - nr_failed++;
> }
>
> stats->nr_failed_pages += nr_pages + nr_retry_pages;
> /* nr_failed isn't updated for not used */
> - nr_large_failed += large_retry;
> stats->nr_thp_failed += thp_retry;
> rc_saved = rc;
> if (list_empty(&unmap_folios))
> @@ -1727,12 +1719,8 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> else
> goto move;
> case -EAGAIN:
> - if (is_large) {
> - large_retry++;
> - thp_retry += is_thp;
> - } else {
> - retry++;
> - }
> + retry++;
> + thp_retry += is_thp;
> nr_retry_pages += nr_pages;
> break;
> case MIGRATEPAGE_SUCCESS:
> @@ -1750,20 +1738,14 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> * removed from migration folio list and not
> * retried in the next outer loop.
> */
> - if (is_large) {
> - nr_large_failed++;
> - stats->nr_thp_failed += is_thp;
> - } else {
> - nr_failed++;
> - }
> -
> + nr_failed++;
> + stats->nr_thp_failed += is_thp;
> stats->nr_failed_pages += nr_pages;
> break;
> }
> }
> }
> nr_failed += retry;
> - nr_large_failed += large_retry;
> stats->nr_thp_failed += thp_retry;
> stats->nr_failed_pages += nr_retry_pages;
> move:
> @@ -1771,17 +1753,15 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> try_to_unmap_flush();
>
> retry = 1;
> - for (pass = 0; pass < nr_pass && (retry || large_retry); pass++) {
> + for (pass = 0; pass < nr_pass && retry; pass++) {
> retry = 0;
> - large_retry = 0;
> thp_retry = 0;
> nr_retry_pages = 0;
>
> dst = list_first_entry(&dst_folios, struct folio, lru);
> dst2 = list_next_entry(dst, lru);
> list_for_each_entry_safe(folio, folio2, &unmap_folios, lru) {
> - is_large = folio_test_large(folio);
> - is_thp = is_large && folio_test_pmd_mappable(folio);
> + is_thp = folio_test_large(folio) && folio_test_pmd_mappable(folio);
> nr_pages = folio_nr_pages(folio);
>
> cond_resched();
> @@ -1797,12 +1777,8 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> */
> switch(rc) {
> case -EAGAIN:
> - if (is_large) {
> - large_retry++;
> - thp_retry += is_thp;
> - } else {
> - retry++;
> - }
> + retry++;
> + thp_retry += is_thp;
> nr_retry_pages += nr_pages;
> break;
> case MIGRATEPAGE_SUCCESS:
> @@ -1810,13 +1786,8 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> stats->nr_thp_succeeded += is_thp;
> break;
> default:
> - if (is_large) {
> - nr_large_failed++;
> - stats->nr_thp_failed += is_thp;
> - } else {
> - nr_failed++;
> - }
> -
> + nr_failed++;
> + stats->nr_thp_failed += is_thp;
> stats->nr_failed_pages += nr_pages;
> break;
> }
> @@ -1825,14 +1796,10 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> }
> }
> nr_failed += retry;
> - nr_large_failed += large_retry;
> stats->nr_thp_failed += thp_retry;
> stats->nr_failed_pages += nr_retry_pages;
>
> - if (rc_saved)
> - rc = rc_saved;
> - else
> - rc = nr_failed + nr_large_failed;
> + rc = rc_saved ? : nr_failed;
> out:
> /* Cleanup remaining folios */
> dst = list_first_entry(&dst_folios, struct folio, lru);