linux-kernel - Re: [PATCH] mm/huge_memory: prevent THP_ZERO_PAGE

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Message-Id: <20220905130728.1e814d185b189faece6f2c2f@linux-foundation.org>
Date:   Mon, 5 Sep 2022 13:07:28 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Liu Shixin <liushixin2@...wei.com>
Cc:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH] mm/huge_memory: prevent THP_ZERO_PAGE_ALLOC increased
 twice

On Mon, 5 Sep 2022 21:38:13 +0800 Liu Shixin <liushixin2@...wei.com> wrote:

> If two or more threads call get_huge_zero_page concurrently, THP_ZERO_PAGE_ALLOC
> may increased two or more times. But actually, this should only count
> as once since the extra zero pages has been freed.

Well, for better of for worse,
Documentation/admin-guide/mm/transhuge.rst says

thp_zero_page_alloc
	is incremented every time a huge zero page is
	successfully allocated. It includes allocations which where
	dropped due race with other allocation. Note, it doesn't count
	every map of the huge zero page, only its allocation.

If you think this interprtation should be changed then please explain
why, and let's be sure to update the documentation accordingly.