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Date:   Sat, 25 Jun 2022 02:19:44 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     cgel.zte@gmail.com
Cc:     viro@zeniv.linux.org.uk, hughd@google.com, ran.xiaokai@zte.com.cn,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH] drop caches: skip tmpfs and ramfs
Message-ID: <YrbTMJAuwY59CwRS@infradead.org>
References: <20220624182121.995294-1-ran.xiaokai@zte.com.cn>
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On Fri, Jun 24, 2022 at 06:21:21PM +0000, cgel.zte@gmail.com wrote:
> From: Ran Xiaokai <ran.xiaokai@zte.com.cn>
> 
> All tmpfs and ramfs pages have PG_dirty bit set
> once they are allocated and added to the pagecache。So pages
> can not be freed from tmpfs or ramfs. So skip tmpfs and ramfs
> when drop caches.

Hard coding magic constants in VFS code is a bad idea.  If you have
numbers to justify this change (which should go into this commit log),
it can be properly solved by a flag on the super block,
file_system_type or even better bdi.