On Fri, May 14, 2010 at 05:24:18PM +1000, Dave Chinner wrote:
> This series reworks the filesystem shrinkers. We currently have a
> set of issues with the current filesystem shrinkers:
> 1. There is an dependency between dentry and inode cache
> shrinking that is only implicitly defined by the order of
> shrinker registration.
> 2. The shrinkers need to walk the superblock list and pin
> the superblock to avoid unmount races with the sb going
> 3. The dentry cache uses per-superblock LRUs and proportions
> reclaim between all the superblocks which means we are
> doing breadth based reclaim. This means we touch every
> superblock for every shrinker call, and may only reclaim
> a single dentry at a time from a given superblock.
> 4. The inode cache has a global LRU, so it has different
> reclaim patterns to the dentry cache, despite the fact
> that the dentry cache is generally the only thing that
> pins inodes in memory.
> 5. Filesystems need to register their own shrinkers for
> caches and can't co-ordinate them with the dentry and
> inode cache shrinkers.
NAK in that form; sb refcounting and iterators had been reworked for .34,
so at least it needs rediff on top of that. What's more, it's very
obviously broken wrt locking - you are unregistering a shrinker
from __put_super(). I.e. grab rwsem exclusively under a spinlock.
Essentially, you've turned dropping a _passive_ reference to superblock
(currently an operation safe in any context) into an operation allowed
only when no fs or vm locks are held by caller. Not going to work...