linux-kernel - Re: [RFC PATCH 1/1] mm: only use old generation and stable tier for madv

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Date:   Fri, 13 Oct 2023 16:38:28 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Michal Hocko <mhocko@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Zhaoyang Huang <huangzhaoyang@...il.com>, steve.kang@...soc.com
Subject: Re: [RFC PATCH 1/1] mm: only use old generation and stable tier for
 madv_pageout

On Fri, Oct 13, 2023 at 07:30:28PM +0800, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> 
> Dropping pages of young generation or unstable tier via madvise could
> make the system experience heavy page thrashing and IO pressure.

... then userspace should not do that?

> @@ -5091,6 +5091,7 @@ static int get_tier_idx(struct lruvec *lruvec, int type)
>  
>  	return tier - 1;
>  }
> +EXPORT_SYMBOL_GPL(get_tier_idx);

Why would this need to be exported to modules in order to be used by
madvise?  Is this patch just a trojan horse so you can use get_tier_idx
in your own module?  NAK.