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

[David Hildenbrand]

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