linux-kernel - Re: [PATCH v2] mm/page_isolation: do not isolate the max order page

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Message-ID: <46fcf0c1-7c38-723b-8905-953d72f1d6bc@redhat.com>
Date:   Thu, 3 Dec 2020 17:28:00 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Muchun Song <songmuchun@...edance.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v2] mm/page_isolation: do not isolate the max order page

On 03.12.20 17:22, Muchun Song wrote:
> The max order page has no buddy page and never merge to other order.
> So isolating and then freeing it is pointless. And if order == MAX_ORDER
> - 1, then the buddy can actually be a !pfn_valid() in some corner case?
> pfn_valid_within(buddy_pfn) that follows would only catch it on archs
> with holes in zone. Then is_migrate_isolate_page(buddy) might access an
> invalid buddy. So this is also a bug fix.
> 
> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")

As just replied to v1, I don't think this is required and the patch
description can be simplified - e.g., stating that we have/had not such
users.


-- 
Thanks,

David / dhildenb