linux-kernel - Re: [PATCH] fs: drop_caches: draining pages before dropping caches

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Message-ID: <20230703-freifahrt-dachwohnung-49d858588e88@brauner>
Date:   Mon, 3 Jul 2023 12:16:57 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Andrew Yang <andrew.yang@...iatek.com>, linux-mm@...ck.org
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        wsd_upstream@...iatek.com, casper.li@...iatek.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] fs: drop_caches: draining pages before dropping caches

Really more suitable for -mm to review.

On Fri, Jun 30, 2023 at 05:22:02PM +0800, Andrew Yang wrote:
> We expect a file page access after dropping caches should be a major
> fault, but sometimes it's still a minor fault. That's because a file
> page can't be dropped if it's in a per-cpu pagevec. Draining all pages
> from per-cpu pagevec to lru list before trying to drop caches.
> 
> Signed-off-by: Andrew Yang <andrew.yang@...iatek.com>
> ---
>  fs/drop_caches.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/drop_caches.c b/fs/drop_caches.c
> index e619c31b6bd9..b9575957a7c2 100644
> --- a/fs/drop_caches.c
> +++ b/fs/drop_caches.c
> @@ -10,6 +10,7 @@
>  #include <linux/writeback.h>
>  #include <linux/sysctl.h>
>  #include <linux/gfp.h>
> +#include <linux/swap.h>
>  #include "internal.h"
>  
>  /* A global variable is a bit ugly, but it keeps the code simple */
> @@ -59,6 +60,7 @@ int drop_caches_sysctl_handler(struct ctl_table *table, int write,
>  		static int stfu;
>  
>  		if (sysctl_drop_caches & 1) {
> +			lru_add_drain_all();
>  			iterate_supers(drop_pagecache_sb, NULL);
>  			count_vm_event(DROP_PAGECACHE);
>  		}
> -- 
> 2.18.0
>