linux-kernel - Re: [patch 52/52] fs: icache less I

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Message-ID: <20100701033342.GT24712@dastard>
Date:	Thu, 1 Jul 2010 13:33:42 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	John Stultz <johnstul@...ibm.com>,
	Frank Mayhar <fmayhar@...gle.com>
Subject: Re: [patch 52/52] fs: icache less I_FREEING time

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@...e.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@...morbit.com
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