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

[Zi Yan <ziy@nvidia.com>]

On 20 May 2025, at 9:20, David Hildenbrand wrote:

>>> if a page gets freed while the pageblock is isolated, it cannot get added to the list of an owner easily.
>>
>> Right. In theory, it is possible, since when a MIGRATED_ISOLATE page is freed,
>> __free_one_page() can find its buddy and add the freed page to its buddy's
>> buddy_list without performing a merge like current code. But it needs a new
>> code path in __add_to_free_list(), since it is not added to the head nor the
>> tail of a free list.
>
> But what if the whole pageblock gets freed in a single shot (IOW, there is no buddy to lookup the list for?).

You are right. This means when MIGRATE_ISOLATE is removed, the global
MIGRATE_ISOLATE free list stays. BTW, looking at struct free_area,
its nr_free accounts for free pages in all migratetypes. Either struct free_area
stays the same or more code changes are needed to have isolated free list
+ !isolated free list. I will try to figure this out in the follow-up patchset.

--
Best Regards,
Yan, Zi