On 8/21/2023 10:20 AM, Huang, Ying wrote:
> Baolin Wang <[email protected]> writes:
>
>> Now there are 3 places will validate if a page can mirate or not, and
>> some validations are performed later, which will waste some CPU to call
>> numa_migrate_prep().
>>
>> Thus we can move all the migration validation into numa_migrate_prep(),
>> which is more maintainable as well as saving some CPU resources. Another
>> benefit is that it can serve as a preparation for supporting batch migration
>> in do_numa_page() in future.
>>
>> Signed-off-by: Baolin Wang <[email protected]>
>> ---
>> mm/memory.c | 19 +++++++++++++++++++
>> mm/migrate.c | 19 -------------------
>> 2 files changed, 19 insertions(+), 19 deletions(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index d003076b218d..bee9b1e86ef0 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -4747,6 +4747,25 @@ int numa_migrate_prep(struct page *page, struct vm_area_struct *vma,
>> *flags |= TNF_FAULT_LOCAL;
>> }
>>
>> + /*
>> + * Don't migrate file pages that are mapped in multiple processes
>> + * with execute permissions as they are probably shared libraries.
>> + */
>> + if (page_mapcount(page) != 1 && page_is_file_lru(page) &&
>> + (vma->vm_flags & VM_EXEC))
>> + return NUMA_NO_NODE;
>> +
>> + /*
>> + * Also do not migrate dirty pages as not all filesystems can move
>> + * dirty pages in MIGRATE_ASYNC mode which is a waste of cycles.
>> + */
>> + if (page_is_file_lru(page) && PageDirty(page))
>> + return NUMA_NO_NODE;
>> +
>> + /* Do not migrate THP mapped by multiple processes */
>> + if (PageTransHuge(page) && total_mapcount(page) > 1)
>> + return NUMA_NO_NODE;
>> +
>> return mpol_misplaced(page, vma, addr);
>
> In mpol_misplaced()->should_numa_migrate_memory(), accessing CPU and PID
> will be recorded. So the code change above will introduce some behavior
> change.
Indeed.
>
> How about move these checks into a separate function which is called
> between numa_migrate_prep() and migrate_misplaced_page() after unlocking
> PTL?
Sounds reasonable to me. Thanks for your input.
>
> --
> Best Regards,
> Huang, Ying
>
>> }
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index e21d5a7e7447..9cc98fb1d6ec 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -2485,10 +2485,6 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
>>
>> VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);
>>
>> - /* Do not migrate THP mapped by multiple processes */
>> - if (PageTransHuge(page) && total_mapcount(page) > 1)
>> - return 0;
>> -
>> /* Avoid migrating to a node that is nearly full */
>> if (!migrate_balanced_pgdat(pgdat, nr_pages)) {
>> int z;
>> @@ -2533,21 +2529,6 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
>> LIST_HEAD(migratepages);
>> int nr_pages = thp_nr_pages(page);
>>
>> - /*
>> - * Don't migrate file pages that are mapped in multiple processes
>> - * with execute permissions as they are probably shared libraries.
>> - */
>> - if (page_mapcount(page) != 1 && page_is_file_lru(page) &&
>> - (vma->vm_flags & VM_EXEC))
>> - goto out;
>> -
>> - /*
>> - * Also do not migrate dirty pages as not all filesystems can move
>> - * dirty pages in MIGRATE_ASYNC mode which is a waste of cycles.
>> - */
>> - if (page_is_file_lru(page) && PageDirty(page))
>> - goto out;
>> -
>> isolated = numamigrate_isolate_page(pgdat, page);
>> if (!isolated)
>> goto out;