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

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Date:   Mon, 1 Mar 2021 14:50:07 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Yu Zhao <yuzhao@...gle.com>, 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 12:13:14PM +0000, Matthew Wilcox wrote:
> 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.

+1 to this.

The problem with compound_head() is systemic and ad-hoc solution to few
page flags will only complicate the picture.

-- 
 Kirill A. Shutemov