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

[Zi Yan]

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.

> Oh well. So it's still a migratetype, but the pageblock handling is now
> different.

Yep. We also have PB_migrate_skip, a bit in pageblock_bits used for memory
compaction and not part of migratetype.

--
Best Regards,
Yan, Zi