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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Zi Yan <ziy@nvidia.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, Xin Hao <xhao@linux.alibaba.com>,
        Yang Shi <shy828301@gmail.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        "Oscar Salvador" <osalvador@suse.de>,
        Alistair Popple <apopple@nvidia.com>
Subject: Re: [PATCH 1/2] migrate_pages_batch: simplify retrying and failure
 counting of large folios
References: <20230509022014.380493-1-ying.huang@intel.com>
        <21078C33-2679-4C13-B46D-65858A4DC516@nvidia.com>
Date:   Wed, 10 May 2023 10:36:24 +0800
In-Reply-To: <21078C33-2679-4C13-B46D-65858A4DC516@nvidia.com> (Zi Yan's
        message of "Tue, 09 May 2023 10:25:44 -0400")
Message-ID: <875y90ap5j.fsf@yhuang6-desk2.ccr.corp.intel.com>
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Zi Yan <ziy@nvidia.com> writes:

> On 8 May 2023, at 22:20, Huang Ying wrote:
>
>> 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.
>>
>> 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);
>
> Should this be part of patch 2? Or maybe just merge two patches?

OK.  Will merge 2 patches.

>>  			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);
>> -- 
>> 2.39.2
>
> Otherwise LGTM. Reviewed-by: Zi Yan <ziy@nvidia.com>

Thanks!

Best Regards,
Huang, Ying