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Message-ID: <bfae7d17-eb50-55b1-1275-5ba0f86a5273@redhat.com>
Date:   Tue, 1 Mar 2022 17:22:08 +0100
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Subject: Re: [PATCH] mm: split vm_normal_pages for LRU and non-LRU handling
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To:     Felix Kuehling <felix.kuehling@amd.com>,
        Alex Sierra <alex.sierra@amd.com>, jgg@nvidia.com
Cc:     linux-mm@kvack.org, rcampbell@nvidia.com,
        linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        hch@lst.de, jglisse@redhat.com, apopple@nvidia.com,
        willy@infradead.org, akpm@linux-foundation.org
References: <20220218192640.GV4160@nvidia.com>
 <20220228203401.7155-1-alex.sierra@amd.com>
 <2a042493-d04d-41b1-ea12-b326d2116861@redhat.com>
 <41469645-55be-1aaa-c1ef-84a123fdb4ea@amd.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <41469645-55be-1aaa-c1ef-84a123fdb4ea@amd.com>
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>>
>>>   		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