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From:   Alistair Popple <apopple@nvidia.com>
To:     Huang Ying <ying.huang@intel.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Xin Hao <xhao@linux.alibaba.com>,
        Zi Yan <ziy@nvidia.com>, Yang Shi <shy828301@gmail.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Oscar Salvador <osalvador@suse.de>
Subject: Re: [PATCH 1/2] migrate_pages_batch: simplify retrying and failure
 counting of large folios
Date:   Tue, 09 May 2023 14:33:07 +1000
In-reply-to: <20230509022014.380493-1-ying.huang@intel.com>
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Huang Ying <ying.huang@intel.com> 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@nvidia.com>

> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Cc: Xin Hao <xhao@linux.alibaba.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: Alistair Popple <apopple@nvidia.com>
> ---
>  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);