linux-kernel - Re: [PATCH v4 0/4] Make MIGRATE

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Message-ID: <fed40607-edcd-4338-85ae-7656a374728b@suse.cz>
Date: Sat, 17 May 2025 22:26:48 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Zi Yan <ziy@...dia.com>, David Hildenbrand <david@...hat.com>,
 Oscar Salvador <osalvador@...e.de>, Johannes Weiner <hannes@...xchg.org>,
 linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 Mel Gorman <mgorman@...hsingularity.net>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Brendan Jackman <jackmanb@...gle.com>, Richard Chang
 <richardycc@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/4] Make MIGRATE_ISOLATE a standalone bit

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.