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

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Message-ID: <BF76B420-C221-43A7-8D07-37863C850FAC@nvidia.com>
Date: Tue, 20 May 2025 10:07:18 -0400
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...hat.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 May 2025, at 9:33, David Hildenbrand wrote:

> 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.

Yep,

struct free_area {
	struct list_head	free_list[MIGRATE_TYPES];
	struct list_head	isolate_list;
	unsigned long		nr_free;
};

--
Best Regards,
Yan, Zi