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

[Li Wang]

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.

On 2013/12/17 11:58, Matthew Wilcox wrote:
> On Tue, Dec 17, 2013 at 11:08:16AM +0800, Li Wang wrote:
> > As far as we know, fadvise(DONTNEED) does not support metadata
> > cache cleaning. We think that is desirable under massive small files
> > situations. Another thing is that do people accept the behavior
> > of feeding a directory fd to fadvise will recusively clean all
> > page caches of files inside that directory?
>
> I think there's a really good permissions-related question here.
> If that's an acceptable interface, should one have to be CAP_SYS_ADMIN
> to issue the request?  What if some of the files below this directory
> are not owned by the user issuing the request?
>
> > On 2013/12/17 1:45, Cong Wang wrote:
> > > On Mon, Dec 16, 2013 at 7:00 AM, Li Wang <liwang@xxxxxxxxxxxxxxx> wrote:
> > > > This patch extend the 'drop_caches' interface to
> > > > support directory level cache cleaning and has a complete
> > > > backward compatibility. '{1,2,3}' keeps the same semantics
> > > > as before. Besides, "{1,2,3}:DIRECTORY_PATH_NAME" is allowed
> > > > to recursively clean the caches under DIRECTORY_PATH_NAME.
> > > > For example, 'echo 1:/home/foo/jpg > /proc/sys/vm/drop_caches'
> > > > will clean the page caches of the files inside 'home/foo/jpg'.
> > >
> > > This interface is ugly...
> > >
> > > And we already have a file-level drop cache, that is,
> > > fadvise(DONTNEED). Can you extend it if it can't
> > > handle a directory fd?
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