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SubjectRe: [PATCH 1/3] mm: migrate: Fix the return value of migrate_pages()
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On 2021/11/24 2:46, Mike Kravetz wrote:
> On 11/7/21 01:57, Baolin Wang wrote:
>> As Zi Yan pointed out, the syscall move_pages() can return a non-migrated
>> number larger than the number of pages the users tried to migrate, when a
>> THP page is failed to migrate. This is confusing for users.
>>
>> Since other migration scenarios do not care about the actual non-migrated
>> number of pages except the memory compaction migration which will fix in
>> following patch. Thus we can change the return value to return the number
>> of {normal page, THP, hugetlb} instead to avoid this issue, and the number
>> of THP splits will be considered as the number of non-migrated THP, no matter
>> how many subpages of the THP are migrated successfully. Meanwhile we should
>> still keep the migration counters using the number of normal pages.
>>
>> Co-developed-by: Zi Yan <ziy@nvidia.com>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>> ---
>> mm/migrate.c | 63 +++++++++++++++++++++++++++++++++++++++++++++---------------
>> 1 file changed, 47 insertions(+), 16 deletions(-)
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index a11e948..9aafdab 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1428,7 +1428,7 @@ static inline int try_split_thp(struct page *page, struct page **page2,
>> * @mode: The migration mode that specifies the constraints for
>> * page migration, if any.
>> * @reason: The reason for page migration.
>> - * @ret_succeeded: Set to the number of pages migrated successfully if
>> + * @ret_succeeded: Set to the number of normal pages migrated successfully if
>> * the caller passes a non-NULL pointer.
>> *
>> * The function returns after 10 attempts or if no pages are movable any more
>> @@ -1436,7 +1436,9 @@ static inline int try_split_thp(struct page *page, struct page **page2,
>> * It is caller's responsibility to call putback_movable_pages() to return pages
>> * to the LRU or free list only if ret != 0.
>> *
>> - * Returns the number of pages that were not migrated, or an error code.
>> + * Returns the number of {normal page, THP} that were not migrated, or an error code.
>> + * The number of THP splits will be considered as the number of non-migrated THP,
>> + * no matter how many subpages of the THP are migrated successfully.
>> */
>> int migrate_pages(struct list_head *from, new_page_t get_new_page,
>> free_page_t put_new_page, unsigned long private,
>> @@ -1445,6 +1447,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>> int retry = 1;
>> int thp_retry = 1;
>> int nr_failed = 0;
>> + int nr_failed_pages = 0;
>> int nr_succeeded = 0;
>> int nr_thp_succeeded = 0;
>> int nr_thp_failed = 0;
>> @@ -1456,13 +1459,16 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>> int swapwrite = current->flags & PF_SWAPWRITE;
>> int rc, nr_subpages;
>> LIST_HEAD(ret_pages);
>> + LIST_HEAD(thp_split_pages);
>> bool nosplit = (reason == MR_NUMA_MISPLACED);
>> + bool no_subpage_counting = false;
>>
>> trace_mm_migrate_pages_start(mode, reason);
>>
>> if (!swapwrite)
>> current->flags |= PF_SWAPWRITE;
>>
>> +thp_subpage_migration:
>> for (pass = 0; pass < 10 && (retry || thp_retry); pass++) {
>> retry = 0;
>> thp_retry = 0;
>> @@ -1511,18 +1517,20 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>> case -ENOSYS:
>> /* THP migration is unsupported */
>> if (is_thp) {
>> - if (!try_split_thp(page, &page2, from)) {
>> + nr_thp_failed++;
>> + if (!try_split_thp(page, &page2, &thp_split_pages)) {
>
> Does thp_split_pages need to be initialized before this call?

The declaration "LIST_HEAD(thp_split_pages);" already did list
initialization, right?

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