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

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Message-ID: <52B019F5.7020505@ubuntukylin.com>
Date:	Tue, 17 Dec 2013 17:31:33 +0800
From:	Li Wang <liwang@...ntukylin.com>
To:	Li Zefan <lizefan@...wei.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

This extension is just add-on extension. The original debugging
capability is still there, and more flexible debugging is now allowed.

On 2013/12/17 17:12, Li Zefan wrote:
> 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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