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 12:58:58 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Matthew Wilcox <willy@...radead.org>, 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 Mon, Mar 01, 2021 at 02:50:07PM +0300, Kirill A. Shutemov wrote:
> 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.

Well, I call it an incremental improvement, and how exactly does it
complicate the picture?

I see your point: you prefer a complete replacement. But my point is
not about the preference; it's about presenting an option: I'm not
saying we have to go with this series; I'm saying if you don't want
to wait, here is something quick but not perfect.