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From:   "Alex Zhu (Kernel)" <alexlzhu@fb.com>
To:     Yang Shi <shy828301@gmail.com>
CC:     Rik van Riel <riel@fb.com>, Kernel Team <Kernel-team@fb.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "willy@infradead.org" <willy@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [PATCH v3] mm: add thp_utilization metrics to
 /proc/thp_utilization
Thread-Topic: [PATCH v3] mm: add thp_utilization metrics to
 /proc/thp_utilization
Thread-Index: AQHYqPrSmG3WqzybNUurgyMbb9mveq2gpnsAgAAD8ACAAAWRgIAAB5EAgASWfICAAAsqAIABevqAgAABMAA=
Date:   Tue, 9 Aug 2022 17:15:47 +0000
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> OK, it is hard to tell what it looks like now. But the THPs on the
> deferred split list may be on the "low utilization split" list too?
> IIUC the major difference is to replace zero-filled subpage to special
> zero page, so you implemented another THP split function to handle it?
> 
> Anyway the code should answer the most questions.

They can indeed end up on both lists. This did have to be handled when 
implementing the shrinker. 

We free the zero filled subpages, while modifying the existing split_huge_page()
function. Will follow up that change in another patch.