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Date: Tue, 17 Dec 2013 17:12:52 +0800
From: Li Zefan <lizefan@huawei.com>
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To: Li Wang <liwang@ubuntukylin.com>
CC: Matthew Wilcox <matthew@wil.cx>, Cong Wang <xiyou.wangcong@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>, Sage Weil <sage@inktank.com>,
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        LKML <linux-kernel@vger.kernel.org>,
        Yunchuan Wen <yunchuanwen@ubuntukylin.com>
Subject: Re: [PATCH 0/5] VFS: Directory level cache cleaning
References: <cover.1387205337.git.liwang@ubuntukylin.com> <CAM_iQpUSX1yX9SMvUnbwZ7UkaBMUheOEiZNaSb4m8gWBQzzGDQ@mail.gmail.com> <52AFC020.10403@ubuntukylin.com> <20131217035847.GA10392@parisc-linux.org> <52AFFBE3.8020507@ubuntukylin.com>
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On 2013/12/17 15:23, Li Wang wrote:
> If we do wanna equip fadvise() with directory level page cache cleaning,
> this could be solved by invoking (inode_permission() || capable(CAP_SYS_ADMIN)) before manipulating the page cache of that inode.
> We think the current extension to 'drop_caches' has a complete back
> compatibility, the old semantics keep unchanged, and with add-on
> features to do finer granularity cache cleaning should be also
> desirable.
> 

I don't think you can extend the drop_caches interface this way. It should
be used for debuging only.

commit 9d0243bca345d5ce25d3f4b74b7facb3a6df1232
Author: Andrew Morton <akpm@osdl.org>
Date:   Sun Jan 8 01:00:39 2006 -0800

    [PATCH] drop-pagecache

    Add /proc/sys/vm/drop_caches.  When written to, this will cause the kernel to
    discard as much pagecache and/or reclaimable slab objects as it can.  THis
    operation requires root permissions.

    ...

    This is a debugging feature: useful for getting consistent results between
    filesystem benchmarks.  We could possibly put it under a config option, but
    it's less than 300 bytes.

Also see http://lkml.org/lkml/2013/7/26/230