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

[Michal Hocko]

On Tue 17-12-13 17:12:52, 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.

Completely agreed. The interface shouldn't be further extended. I would
even argue it shouldn't be used in the first place.

> commit 9d0243bca345d5ce25d3f4b74b7facb3a6df1232
> Author: Andrew Morton <akpm@xxxxxxxx>
> 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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-- 
Michal Hocko
SUSE Labs
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