Re: [PATCH] fs: allow for fs-specific objects to be pruned as part of pruning inodes

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 24 Jan 2013 00:32:31 +1100 Dave Chinner <david@fromorbit.com> wrote:

> Also, the superblock shrinker is designed around a direct 1:1:1
> dependency relationship between the superblock dentry, inode and "fs
> cache" objects. i.e. dentry pins inode pins fs cache object.  It is
> designed to keep a direct balance of the three caches by ensuring
> they get scanned in amounts directly proportional to the relative
> differences in their object counts.  That can't be done with
> separate shrinkers, hence the use of the superblock shrinker to
> define the dependent relationship between the caches.

I was staring at the code and at the 0e1fdafd9 changelog trying to work
out why prune_super() does its weird shrinker-in-a-shrinker thing.  And
failing.

IOW it needs a code comment, please.  Ideally one which explains *why*
"It is designed to keep a direct balance of the three caches...".  What
would go wrong if the fs were to just register its own shrinker in the
expected manner?