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

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Message-ID: <39861ba3-078e-40ad-bb9e-43baff981ac9@redhat.com>
Date: Tue, 20 May 2025 15:33:56 +0200
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>
Cc: Vlastimil Babka <vbabka@...e.cz>, Oscar Salvador <osalvador@...e.de>,
 Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
 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 20.05.25 15:31, Zi Yan wrote:
> 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?).
> 

And thinking about it, another problem is if a page gets freed that has 
no buddies.

> You are right. This means when MIGRATE_ISOLATE is removed, the global
> MIGRATE_ISOLATE free list stays.

Right. We could just have that one separately from the existing array.

-- 
Cheers,

David / dhildenb