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

From: Kefeng Wang <wangkefeng.wang@huawei.com>
To: David Hildenbrand <david@redhat.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 14:53:21 +0800	[thread overview]
Message-ID: <9bb17dcd-4651-41d2-9982-4632147a82f8@huawei.com> (raw)
In-Reply-To: <ff4e0024-c256-46e9-a203-ad62c21896f7@redhat.com>

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?

But after v5.13 commit 782276b4d0ad ("arm64: Force SPARSEMEM_VMEMMAP
as the only memory management model"), it looks only old lts, eg, 5.10 
could meet this issue.