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 12:49:41 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     Matthew Wilcox <willy@...radead.org>
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 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.

I hasn't been following the effort closely, so I'm rereading the very
first discussion "Are THPs the right model for the pagecache?" and
then I need to rewatch the recorded Zoom meeting. As I said I'm on
board with the idea, but I can't create a roadmap based on my current
rough understanding, unless you prefer me to just randomly throw some
reviewed-bys at your patches in the next few days. (Our long-term plan
for folios is to support arbitrary anon page sizes because anon memory
is more than 90% of total user memory on Android, Chrome OS and in our
data centers.)

That said, if you have something ready to test, we could do it for you
in our runtime environments immediately.