Re: [PATCH 0/5] Per superblock shrinkers V2

Andrew Morton
2010-05-27T20:30:18Z

On Tue, 25 May 2010 18:53:03 +1000
Dave Chinner <david@fromorbit.com> 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
> away.
> 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.

Nice description, but... it never actually told us what the benefit of
the changes are. Presumably some undescribed workload had some
undescribed user-visible problem. But what was that workload, and what
was the user-visible problem, and how does the patch affect all this?

Stuff like that.