Re: SLUB defrag pull request?

[Miklos Szeredi <miklos@szeredi.hu>]

On Tue, 21 Oct 2008, Christoph Lameter wrote:
> The only way that a secure reference can be established is if the
> slab page is locked. That requires a spinlock. The slab allocator
> calls the get() functions while the slab lock guarantees object
> existence. Then locks are dropped and reclaim actions can start with
> the guarantee that the slab object will not suddenly vanish.

Yes, you've made up your mind, that you want to do it this way.  But
it's the _wrong_ way, this "want to get a secure reference for use
later" leads to madness when applied to dentries or inodes.  Try for a
minute to think outside this template.

For example dcache_lock will protect against dentries moving to/from
d_lru.  So you can do this:

  take dcache_lock
  check if d_lru is non-empty
  take sb->s_umount
  free dentry
  release sb->s_umount
  release dcache_lock

Yeah, locking will be more complicated in reality.  Still, much less
complicated than trying to do the same across two separate phases.

Why can't something like that work?

Miklos

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>