Re: [RFC 1/6] mm/migrate_pages: separate huge page and normal pages migration

Huang, Ying
2022-09-22T06:23:02Z

Baolin Wang <baolin.wang@linux.alibaba.com> writes:

> On 9/21/2022 2:06 PM, Huang Ying wrote:
>> This is a preparation patch to batch the page unmapping and moving for
>> the normal pages and THPs. Based on that we can batch the TLB
>> shootdown during the page migration and make it possible to use some
>> hardware accelerator for the page copying.
>> In this patch the huge page (PageHuge()) and normal page and THP
>> migration is separated in migrate_pages() to make it easy to change
>> the normal page and THP migration implementation.
>> 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>
>> ---
>> mm/migrate.c | 73 +++++++++++++++++++++++++++++++++++++++++++++-------
>> 1 file changed, 64 insertions(+), 9 deletions(-)
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 571d8c9fd5bc..117134f1c6dc 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1414,6 +1414,66 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>> trace_mm_migrate_pages_start(mode, reason);
>> + for (pass = 0; pass < 10 && retry; pass++) {
>> + retry = 0;
>> +
>> + list_for_each_entry_safe(page, page2, from, lru) {
>> + nr_subpages = compound_nr(page);
>> + cond_resched();
>> +
>> + if (!PageHuge(page))
>> + continue;
>> +
>> + rc = unmap_and_move_huge_page(get_new_page,
>> + put_new_page, private, page,
>> + pass > 2, mode, reason,
>> + &ret_pages);
>> + /*
>> + * The rules are:
>> + * Success: hugetlb page will be put back
>> + * -EAGAIN: stay on the from list
>> + * -ENOMEM: stay on the from list
>> + * -ENOSYS: stay on the from list
>> + * Other errno: put on ret_pages list then splice to
>> + * from list
>> + */
>> + switch(rc) {
>> + case -ENOSYS:
>> + /* Hugetlb migration is unsupported */
>> + nr_failed++;
>> + nr_failed_pages += nr_subpages;
>> + list_move_tail(&page->lru, &ret_pages);
>> + break;
>> + case -ENOMEM:
>> + /*
>> + * When memory is low, don't bother to try to migrate
>> + * other pages, just exit.
>> + */
>> + nr_failed++;
>> + nr_failed_pages += nr_subpages + nr_retry_pages;
>> + goto out;
>> + case -EAGAIN:
>> + retry++;
>> + nr_retry_pages += nr_subpages;
>> + break;
>> + case MIGRATEPAGE_SUCCESS:
>> + nr_succeeded += nr_subpages;
>> + break;
>> + default:
>> + /*
>> + * Permanent failure (-EBUSY, etc.):
>> + * unlike -EAGAIN case, the failed page is
>> + * removed from migration page list and not
>> + * retried in the next outer loop.
>> + */
>> + nr_failed++;
>> + nr_failed_pages += nr_subpages;
>> + break;
>> + }
>> + }
>> + }
>> + nr_failed += retry;
>
> Seems we should also record the nr_retry_pages? since the second loop
> will reset the nr_retry_pages.
>
> nr_failed_pages += nr_retry_pages;

Good catch! Will do that in the next version.

> Besides, I also agree with Zi Yan's comment to simplify this larger
> function.

Yes. I think so too.

Best Regards,
Huang, Ying