Re: [PATCH v1 3/5] mm/page_alloc: always move pages to the tail of the freelist in unset_migratetype_isolate()

David Hildenbrand
2020-10-02T15:20:26Z

On 02.10.20 15:24, Michal Hocko wrote:
> On Mon 28-09-20 20:21:08, David Hildenbrand wrote:
>> Page isolation doesn't actually touch the pages, it simply isolates
>> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>>
>> We already place pages to the tail of the freelists when undoing
>> isolation via __putback_isolated_page(), let's do it in any case
>> (e.g., if order <= pageblock_order) and document the behavior.
>>
>> Add a "to_tail" parameter to move_freepages_block() but introduce a
>> a new move_to_free_list_tail() - similar to add_to_free_list_tail().
>>
>> This change results in all pages getting onlined via online_pages() to
>> be placed to the tail of the freelist.
>
> Is there anything preventing to do this unconditionally? Or in other
> words is any of the existing callers of move_freepages_block benefiting
> from adding to the head?

1. mm/page_isolation.c:set_migratetype_isolate()

We move stuff to the MIGRATE_ISOLATE list, we don't care about the order
there.

2. steal_suitable_fallback():

I don't think we care too much about the order when already stealing
pageblocks ... and the freelist is empty I guess?

3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock()

Not sure if we really care.

Good question, I tried to be careful of what I touch. Thoughts?

--
Thanks,

David / dhildenb