linux-kernel - Re: [RFC PATCH 4/5] mm: add page implyreclaim flag

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Message-ID: <ZSKNhZldD8P3l7hA@casper.infradead.org>
Date:   Sun, 8 Oct 2023 12:07:49 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Lincheng Yang <lincheng.yang@...nssion.corp-partner.google.com>
Cc:     akpm@...ux-foundation.org, rostedt@...dmis.org,
        mhiramat@...nel.org, hughd@...gle.com, peterx@...hat.com,
        mike.kravetz@...cle.com, jgg@...pe.ca, surenb@...gle.com,
        steven.price@....com, pasha.tatashin@...een.com,
        kirill.shutemov@...ux.intel.com, yuanchu@...gle.com,
        david@...hat.com, mathieu.desnoyers@...icios.com,
        dhowells@...hat.com, shakeelb@...gle.com, pcc@...gle.com,
        tytso@....edu, 42.hyeyoo@...il.com, vbabka@...e.cz,
        catalin.marinas@....com, lrh2000@....edu.cn, ying.huang@...el.com,
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        findns94@...il.com, neilb@...e.de, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, wanbin.wang@...nssion.com,
        chunlei.zhuang@...nssion.com, jinsheng.zhao@...nssion.com,
        jiajun.ling@...nssion.com, dongyun.liu@...nssion.com,
        Lincheng Yang <lincheng.yang@...nssion.com>
Subject: Re: [RFC PATCH 4/5] mm: add page implyreclaim flag

On Sun, Oct 08, 2023 at 05:59:23PM +0800, Lincheng Yang wrote:
> Add implyrecalim flag means that the page is reclaim from the user advise.
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index a2c83c0100aa..4a1278851d4b 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -138,6 +138,7 @@ enum pageflags {
>  #endif
>  	PG_hot,
>  	PG_cold,
> +	PG_implyreclaim,
>  	__NR_PAGEFLAGS,

Can you do all of this without adding three page flags?  We're really
tight on page flags.  At a minimum, this is going to have to go behind
an ifdef that depends on 64BIT, but it'd be better if we can derive
hot/cold/implyreclaim from existing page flags.  Look at the antics
we go through for PG_young and PG_idle; if we had two page flags free,
we'd spend them on removing the special cases there.