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

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Date:   Fri, 4 Dec 2020 18:12:55 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [External] Re: [PATCH v2] mm/page_isolation: do not isolate the
 max order page

On 04.12.20 17:12, Muchun Song wrote:
> On Fri, Dec 4, 2020 at 12:28 AM David Hildenbrand <david@...hat.com> wrote:
>>
>> 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
> 
> You mean we should remove the Fixes tag? Thanks.

As discussed in v1, I don't think we really have systems where this
applies, but could be in corner cases on MIPS or with FLATMEM. Let's
just leave it like that. :)

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb