Date: Thu, 1 Jul 2010 13:33:42 +1000
From: Dave Chinner <david@fromorbit.com>
To: Nick Piggin <npiggin@suse.de>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
       John Stultz <johnstul@us.ibm.com>, Frank Mayhar <fmayhar@google.com>
Subject: Re: [patch 52/52] fs: icache less I_FREEING time
Message-ID: <20100701033342.GT24712@dastard>
References: <20100624030212.676457061@suse.de>
 <20100624030734.042332166@suse.de>
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 <20100630121452.GG21358@laptop>
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On Wed, Jun 30, 2010 at 10:14:52PM +1000, Nick Piggin wrote:
> On Wed, Jun 30, 2010 at 08:13:54PM +1000, Dave Chinner wrote:
> > On Thu, Jun 24, 2010 at 01:03:04PM +1000, npiggin@suse.de wrote:
> > > Problem with inode reclaim is that it puts inodes into I_FREEING state
> > > and then continues to gather more, during which it may iput,
> > > invalidate_mapping_pages, be preempted, etc. Holding these inodes in
> > > I_FREEING can cause pauses.
> > 
> > What sort of pauses? I can't see how holding a few inodes in
> > I_FREEING state would cause any serious sort of holdoff...
> 
> Well if the inode is accessed again, it has to wait for potentially
> hundreds of inodes to be found from the LRU, pagecache invalidated,
> and destroyed.

So it's a theoretical concern you have, not something that's
actually been demonstrated as a problem?

As it is, If the inode is accessed immediately after teardown has
started, then we failed to hold on to the inode at a higher level
for long enough. Changing the I_FREEING behaviour is trying to
address the issue at the wrong level...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
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