linux-kernel - Re: SLUB defrag pull request?

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Date:	Mon, 20 Oct 2008 20:01:58 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	cl@...ux-foundation.org
CC:	miklos@...redi.hu, penberg@...helsinki.fi, nickpiggin@...oo.com.au,
	hugh@...itas.com, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: SLUB defrag pull request?

On Mon, 20 Oct 2008, Christoph Lameter wrote:
> >> kick_inodes() only works on inodes that first have undergone 
> >> get_inodes() where we establish a refcount under inode_lock(). The final 
> >> cleanup in kick_inodes() is done under iprune_mutex. You are looking at 
> >> the loop that does writeback and invalidates attached dentries. This can 
> >> fail for various reasons.
> > 
> > Yes, but I'm not at all sure that calling remove_inode_buffers() or
> > invalidate_mapping_pages() is OK on a live inode.  They should be done
> > after checking the refcount, just like prune_icache() does.
> 
> Dont we do the same on a truncate?

Yes, with i_mutex and i_alloc_sem held.

> 
> > Also, while d_invalidate() is not actually wrong here, because you
> > check S_ISDIR(), but it's still the wrong function to use.  You really
> > just want to shrink the children.  Invalidation means: the filesystem
> > found out that the cached inode is invalid, so we want to throw it
> > away.  In the future it might actually be able to do it for
> > directories as well, but currently it cannot because of possible
> > mounts on the dentry.
> 
> Thats the same issue as with the dentries. The new function could deal with
> both situations?

Sure.

The big issue is dealing with umount.  You could do something like
grab_super() on sb before getting a ref on the inode/dentry.  But I'm
not sure this is a good idea.  There must be a simpler way to achieve
this...

Miklos
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