linux-kernel - Re: SLUB defrag pull request?

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Message-ID: <48FC9CCC.3040006@linux-foundation.org>
Date:	Mon, 20 Oct 2008 09:59:24 -0500
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Miklos Szeredi <miklos@...redi.hu>
CC:	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?

Miklos Szeredi wrote:
> 
>>> It should be the other way round: first make sure nothing is
>>> referencing the inode, and _then_ start cleaning it up with
>>> appropriate locks held.  See prune_icache().

The code was initially taken from prune_icache.

>> 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?

> 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?


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