Containers and /proc/sys/vm/drop_caches

[Dave Hansen]

On Thu, 2011-01-06 at 14:08 -0800, Matt Helsley wrote:
> Is drop_caches well-defined? IOW would it be permissible to
> not actually drop all or any of the cache entries or to do nothing and
> still report success instead of, say, EPERM, to a container?

It's really just a hint or a request.  It's possible that an

	echo 3 > /proc/sys/vm/drop_caches

returns '2' (for the two bytes written), indicating success and yet, not
a single object was freed.  There's currently no way to tell how much
work it did, or to figure out why it did a certain amount of work.

Frankly, in a container, it probably just shouldn't even show up
in /proc.

-- Dave