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


  • To: Michal Hocko <mhocko@xxxxxxxx>
  • From: David Hildenbrand <david@xxxxxxxxxx>
  • Date: Fri, 2 Oct 2020 17:20:09 +0200
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  • Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, linux-hyperv@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-acpi@xxxxxxxxxxxxxxx, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Oscar Salvador <osalvador@xxxxxxx>, Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>, Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxx>, Vlastimil Babka <vbabka@xxxxxxx>, Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>, Mike Rapoport <rppt@xxxxxxxxxx>, Scott Cheloha <cheloha@xxxxxxxxxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>
  • Delivery-date: Fri, 02 Oct 2020 15:20:31 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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




 


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