linux-kernel - Re: [PATCH] mm/damon: Validate if the pmd entry is present before accessing

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Message-Id: <20220817090722.3a04da77a280c74cccde6b2c@linux-foundation.org>
Date:   Wed, 17 Aug 2022 09:07:22 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     sj@...nel.org, damon@...ts.linux.dev, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/damon: Validate if the pmd entry is present before
 accessing

On Wed, 17 Aug 2022 14:21:12 +0800 Baolin Wang <baolin.wang@...ux.alibaba.com> wrote:

> The pmd_huge() is used to validate if the pmd entry is mapped by a huge
> page, also including the case of non-present (migration or hwpoisoned)
> pmd entry on arm64 or x86 architectures. Thus we should validate if it
> is present before making the pmd entry old or getting young state,
> otherwise we can not get the correct corresponding page.
> 

What are the user-visible runtime effects of this change?