linux-kernel - Re: [PATCH 0/5] VFS: Directory level cache cleaning

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Date:	Tue, 17 Dec 2013 17:12:52 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Li Wang <liwang@...ntukylin.com>
CC:	Matthew Wilcox <matthew@....cx>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Sage Weil <sage@...tank.com>, <linux-fsdevel@...r.kernel.org>,
	<linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Yunchuan Wen <yunchuanwen@...ntukylin.com>
Subject: Re: [PATCH 0/5] VFS: Directory level cache cleaning

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@...l.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

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