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

[Vlastimil Babka]

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