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Date:   Tue, 1 Mar 2022 17:22:08 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Felix Kuehling <felix.kuehling@....com>,
        Alex Sierra <alex.sierra@....com>, jgg@...dia.com
Cc:     linux-mm@...ck.org, rcampbell@...dia.com,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        hch@....de, jglisse@...hat.com, apopple@...dia.com,
        willy@...radead.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] mm: split vm_normal_pages for LRU and non-LRU handling


>>
>>>   		if (PageReserved(page))
>>> diff --git a/mm/migrate.c b/mm/migrate.c
>>> index c31d04b46a5e..17d049311b78 100644
>>> --- a/mm/migrate.c
>>> +++ b/mm/migrate.c
>>> @@ -1614,7 +1614,7 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
>>>   		goto out;
>>>   
>>>   	/* FOLL_DUMP to ignore special (like zero) pages */
>>> -	follflags = FOLL_GET | FOLL_DUMP;
>>> +	follflags = FOLL_GET | FOLL_DUMP | FOLL_LRU;
>>>   	page = follow_page(vma, addr, follflags);
>> Why wouldn't we want to dump DEVICE_COHERENT pages? This looks wrong.
> 
> This function later calls isolate_lru_page, which is something you can't 
> do with a device page.
> 

Then, that code might require care instead. We most certainly don't want
to have random memory holes in a dump just because some anonymous memory
was migrated to DEVICE_COHERENT.

-- 
Thanks,

David / dhildenb

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