linux-kernel - Re: [PATCH v2 5/7] mm: thp: split huge page to any lower order pages.

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Date:   Tue, 8 Aug 2023 11:01:19 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Zi Yan <ziy@...dia.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Yang Shi <shy828301@...il.com>, Yu Zhao <yuzhao@...gle.com>,
        linux-mm@...ck.org
Cc:     "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ryan Roberts <ryan.roberts@....com>,
        Michal Koutný <mkoutny@...e.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Zach O'Keefe <zokeefe@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 5/7] mm: thp: split huge page to any lower order pages.

On 29.03.23 03:17, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.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