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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