Re: [PATCH] mm: memory: use nth_page() in clear/copy_subpage()

From: David Hildenbrand <david@redhat.com>
To: Kefeng Wang <wangkefeng.wang@huawei.com>,
	Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	ziy@nvidia.com, linux-mm@kvack.org
Subject: Re: [PATCH] mm: memory: use nth_page() in clear/copy_subpage()
Date: Tue, 2 Jan 2024 17:11:23 +0100	[thread overview]
Message-ID: <747e1c4e-6339-4b11-aaf9-9f8c4a428d66@redhat.com> (raw)
In-Reply-To: <9bb17dcd-4651-41d2-9982-4632147a82f8@huawei.com>

On 02.01.24 07:53, Kefeng Wang wrote:
> 
> 
> On 2023/12/29 19:15, David Hildenbrand wrote:
>> On 29.12.23 09:49, Matthew Wilcox wrote:
>>> On Fri, Dec 29, 2023 at 04:22:07PM +0800, Kefeng Wang wrote:
>>>> The clear and copy of huge gigantic page has converted to use nth_page()
>>>> to handle the possible discontinuous struct page(SPARSEMEM without
>>>> VMEMMAP),
>>>> but not change for the non-gigantic part, fix it too.
>>>
>>> Can there be discontiguities within a non-gigantic huge page?  My
>>> impression was that you can't have a discontiguity at such a small
>>> boundary.
>>
>> No, we can't. MAX_ORDER allocations from the buddy always completely fit
>> into a memory section.
> 
> On ARM64, we have 32M(16*2M) HugeTLB, it maybe not within a mem section,
> right?

I recall the mem sections are always at least 128 MiB on arm64.

Note that anything > MAX_ORDER is called a "gigantic huge page" in 
hugetlb code.

-- 
Cheers,

David / dhildenb