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From: Ben Myers <bpm@sgi.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: xfs@oss.sgi.com
Subject: Re: [patch 02/12] xfs: do exact log space wakeups in xlog_ungrant_log_space
Date: Thu, 16 Feb 2012 12:36:59 -0600	[thread overview]
Message-ID: <20120216183659.GR7762@sgi.com> (raw)
In-Reply-To: <20111212141433.714245384@bombadil.infradead.org>

On Mon, Dec 12, 2011 at 09:13:49AM -0500, Christoph Hellwig wrote:
> The only reason that xfs_log_space_wake had to do opportunistic wakeups
> was that the old xfs_log_move_tail calling convention didn't allow for
> exact wakeups when not updating the log tail LSN.

Man, that's a doosey. 

when you called xfs_log_move_tail...

if you passed tail_lsn = 1
it would:			not move the tail
				ignore strict accounting and wake only 1

if you passed tail_lsn = 0
it would:			get tail_lsn from l_last_sync_lsn
				move the tail
				pay attention to strict accounting
				wake as many as is correct

if you passed tail_lsn = !1, !0
it would:			move the tail
				pay attention to strict accounting
				wake as many as is correct.

The important thing to understand is that the opportunistic wakeups
would ignore the the test (free_bytes < need_bytes) in
xfs_log_move_tail, so you could wake a process regardless of whether
there is sufficient space in the log for it.  No wonder they had to
pepper the code with opportunistic wakeups to prevent log space hangs... 

> Since this issue has
> been fixed we can do exact wakeups now.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> ---
>  fs/xfs/xfs_log.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: xfs/fs/xfs/xfs_log.c
> ===================================================================
> --- xfs.orig/fs/xfs/xfs_log.c	2011-12-11 15:30:49.977750776 +0100
> +++ xfs/fs/xfs/xfs_log.c	2011-12-11 17:49:00.692836117 +0100
> @@ -2748,7 +2748,7 @@ xlog_ungrant_log_space(xlog_t	     *log,
>  
>  	trace_xfs_log_ungrant_exit(log, ticket);
>  
> -	xfs_log_space_wake(log->l_mp, true);
> +	xfs_log_space_wake(log->l_mp, false);

Yeah, he's doing an _exact_ wakeup now.

Reviewed-by: Ben Myers <bpm@sgi.com>

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  parent reply	other threads:[~2012-02-16 18:36 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-12-12 14:13 [patch 00/12] log grant code cleanups Christoph Hellwig
2011-12-12 14:13 ` [patch 01/12] xfs: split tail_lsn assignments from log space wakeups Christoph Hellwig
2012-01-17 18:48   ` Mark Tinguely
2012-01-25 16:09     ` Christoph Hellwig
2012-02-16 18:21   ` Ben Myers
2012-02-17 19:21     ` Christoph Hellwig
2011-12-12 14:13 ` [patch 02/12] xfs: do exact log space wakeups in xlog_ungrant_log_space Christoph Hellwig
2012-01-17 22:42   ` Mark Tinguely
2012-02-16 18:36   ` Ben Myers [this message]
2011-12-12 14:13 ` [patch 03/12] xfs: remove xfs_trans_unlocked_item Christoph Hellwig
2012-01-23 14:31   ` Mark Tinguely
2012-02-16 18:51     ` Ben Myers
2011-12-12 14:13 ` [patch 04/12] xfs: cleanup xfs_log_space_wake Christoph Hellwig
2012-01-23 19:22   ` Mark Tinguely
2012-01-25 16:10     ` Christoph Hellwig
2012-01-25 19:09       ` Mark Tinguely
2012-01-26 16:13         ` Mark Tinguely
2012-01-26 22:12         ` Dave Chinner
2012-02-16 19:06   ` Ben Myers
2011-12-12 14:13 ` [patch 05/12] xfs: remove log space waitqueues Christoph Hellwig
2012-01-23 21:58   ` Mark Tinguely
2011-12-12 14:13 ` [patch 06/12] xfs: add the xlog_grant_head structure Christoph Hellwig
2012-01-24 15:35   ` Mark Tinguely
2012-02-16 20:23   ` Ben Myers
2011-12-12 14:13 ` [patch 07/12] xfs: add xlog_grant_head_init Christoph Hellwig
2012-01-24 15:43   ` Mark Tinguely
2012-02-16 20:29   ` Ben Myers
2011-12-12 14:13 ` [patch 08/12] xfs: add xlog_grant_head_wake_all Christoph Hellwig
2012-01-24 15:46   ` Mark Tinguely
2012-02-16 20:44   ` Ben Myers
2011-12-12 14:13 ` [patch 09/12] xfs: share code for grant head waiting Christoph Hellwig
2012-01-24 18:10   ` Mark Tinguely
2012-02-16 20:51   ` Ben Myers
2011-12-12 14:13 ` [patch 10/12] xfs: shared code for grant head wakeups Christoph Hellwig
2012-01-24 18:37   ` Mark Tinguely
2012-02-16 21:08   ` Ben Myers
2011-12-12 14:13 ` [patch 11/12] xfs: share code for grant head availability checks Christoph Hellwig
2012-01-24 18:53   ` Mark Tinguely
2012-02-16 21:25   ` Ben Myers
2012-02-17  2:41     ` Dave Chinner
2011-12-12 14:13 ` [patch 12/12] xfs: split and cleanup xfs_log_reserve Christoph Hellwig
2012-02-16 21:36   ` Ben Myers
2012-02-19 21:16     ` Christoph Hellwig
2012-02-16  6:16 ` [patch 00/12] log grant code cleanups Dave Chinner
2012-02-17 18:00   ` Christoph Hellwig
2012-02-16 21:46 ` Ben Myers
2012-02-19 21:17   ` Christoph Hellwig
2012-02-20 21:59     ` Ben Myers
  -- strict thread matches above, loose matches on Subject: below --
2012-02-20  2:31 [PATCH 00/12] log grant code cleanups V2 Christoph Hellwig
2012-02-20  2:31 ` [PATCH 02/12] xfs: do exact log space wakeups in xlog_ungrant_log_space Christoph Hellwig

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