Re: [PATCH v4 0/4] Make MIGRATE_ISOLATE a standalone bit

[David Hildenbrand <david@redhat.com>]

On 18.05.25 02:20, Zi Yan wrote:
> On 17 May 2025, at 16:26, Vlastimil Babka wrote:
> 
>> On 5/9/25 22:01, Zi Yan wrote:
>>> Hi David and Oscar,
>>>
>>> Can you take a look at Patch 2, which changes how online_pages() set
>>> online pageblock migratetypes? It used to first set all pageblocks to
>>> MIGRATE_ISOLATE, then let undo_isolate_page_range() move the pageblocks
>>> to MIGRATE_MOVABLE. After MIGRATE_ISOLATE becomes a standalone bit, all
>>> online pageblocks need to have a migratetype other than MIGRATE_ISOLATE.
>>> Let me know if there is any issue with my changes.
>>>
>>> Hi Johannes,
>>>
>>> Patch 2 now have set_pageblock_migratetype() not accepting
>>> MIGRATE_ISOLATE. I think it makes code better. Thank you for the great
>>> feedback.
>>>
>>> Hi all,
>>>
>>> This patchset moves MIGRATE_ISOLATE to a standalone bit to avoid
>>> being overwritten during pageblock isolation process. Currently,
>>> MIGRATE_ISOLATE is part of enum migratetype (in include/linux/mmzone.h),
>>> thus, setting a pageblock to MIGRATE_ISOLATE overwrites its original
>>> migratetype. This causes pageblock migratetype loss during
>>> alloc_contig_range() and memory offline, especially when the process
>>> fails due to a failed pageblock isolation and the code tries to undo the
>>> finished pageblock isolations.
>>
>> Seems mostly fine to me, just sent suggestion for 4/4.
> 
> Thanks.
> 
>> I was kinda hoping that MIGRATE_ISOLATE could stop being a migratetype. But
>> I also see that it's useful for it to be because then it means it has the
>> freelists in the buddy allocator, can work via __move_freepages_block() etc.
> 
> Yeah, I wanted to remove MIGRATE_ISOLATE from migratetype too, but there
> is a MIGRATE_ISOLATE freelist and /proc/pagetypeinfo also shows isolated
> free pages.

The latter, we can likely fake.

Is there a reasonable way to remove MIGRATE_ISOLATE completely?

Of course, we could simply duplicate the page lists (one set for 
isolated, one set for !isolated), or keep it as is and simply have a
separate one that we separate out. So, we could have a 
migratetype+isolated pair instead.

Just a thought, did not look into all the ugly details.

-- 
Cheers,

David / dhildenb