linux-kernel - Re: [PATCH v2 3/3] mm: use PF_ONLY_HEAD for PG_active and PG

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Date:   Fri, 26 Feb 2021 12:13:14 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     akpm@...ux-foundation.org, alex.shi@...ux.alibaba.com,
        vbabka@...e.cz, guro@...com, hannes@...xchg.org, hughd@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mhocko@...nel.org, vdavydov.dev@...il.com
Subject: Re: [PATCH v2 3/3] mm: use PF_ONLY_HEAD for PG_active and
 PG_unevictable

On Fri, Feb 26, 2021 at 02:17:18AM -0700, Yu Zhao wrote:
> All places but one test, set or clear PG_active and PG_unevictable on
> small or head pages. Use compound_head() explicitly for that singleton
> so the rest can rid of redundant compound_head().

How do you know it's only one place?  I really wish you'd work with me
on folios.  They make the compiler prove that it's not a tail page.