linux-kernel - Re: [patch 15/26] Slab defrag: Support generic defragmentation for inode slab caches

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Message-ID: <Pine.LNX.4.64.0706261119420.18010@schroedinger.engr.sgi.com>
Date:	Tue, 26 Jun 2007 11:21:57 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	suresh.b.siddha@...el.com
Subject: Re: [patch 15/26] Slab defrag: Support generic defragmentation for
 inode slab caches

On Tue, 26 Jun 2007, Andrew Morton wrote:

> > Provide generic functionality that can be used by filesystems that have
> > their own inode caches to also tie into the defragmentation functions
> > that are made available here.
> 
> Yes, this is tricky stuff.  I have vague ancestral memories that the sort
> of inode work which you refer to here can cause various deadlocks, lockdep
> warnings and such nasties when if we attempt to call it from the wrong
> context (ie: from within fs code).

Right that is likelyi the reason why Michael did his stress test...
 
> Possibly we could prevent that by skipping all this code if the caller
> didn't have __GFP_FS.

We do. Look at the earlier patch.

> I trust all the code in kick_inodes() was carefuly copied from 
> prue_icache() and such places - I didn't check it.

Yup tried to remain faithful to that. We could increase the usefulness if 
I could take more liberties with the code in order to actually move an 
item instead of simply reclaiming. But its better to first have a proven 
correct solution before doing more work on that.


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