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Date:   Tue, 8 Aug 2023 11:01:19 +0200
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Subject: Re: [PATCH v2 5/7] mm: thp: split huge page to any lower order pages.
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To:     Zi Yan <ziy@nvidia.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Yang Shi <shy828301@gmail.com>, Yu Zhao <yuzhao@google.com>,
        linux-mm@kvack.org
Cc:     "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Ryan Roberts <ryan.roberts@arm.com>,
        =?UTF-8?Q?Michal_Koutn=c3=bd?= <mkoutny@suse.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Zach O'Keefe <zokeefe@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org
References: <20230329011712.3242298-1-zi.yan@sent.com>
 <20230329011712.3242298-6-zi.yan@sent.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20230329011712.3242298-6-zi.yan@sent.com>
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On 29.03.23 03:17, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> To split a THP to any lower order pages, we need to reform THPs on
> subpages at given order and add page refcount based on the new page
> order. Also we need to reinitialize page_deferred_list after removing
> the page from the split_queue, otherwise a subsequent split will see
> list corruption when checking the page_deferred_list again.
> 
> It has many uses, like minimizing the number of pages after
> truncating a huge pagecache page. For anonymous THPs, we can only split
> them to order-0 like before until we add support for any size anonymous
> THPs.
>

Because I'm currently looking into something that would also not be 
compatible with order-1 for now:

You should make it clear that order-1 is not supported, like:

"mm: thp: split huge page to any lower order pages (except order 1)"

And clarify in the subject why that is the case.

-- 
Cheers,

David / dhildenb