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From: Dave Chinner <david@fromorbit.com>
To: Alex Elder <aelder@sgi.com>
Cc: xfs@oss.sgi.com
Subject: Re: [PATCH 03/34] lib: percpu counter add unless less than functionality
Date: Wed, 22 Dec 2010 14:46:58 +1100	[thread overview]
Message-ID: <20101222034657.GE4907@dastard> (raw)
In-Reply-To: <1292984414.2408.357.camel@doink>

On Tue, Dec 21, 2010 at 08:20:14PM -0600, Alex Elder wrote:
> On Tue, 2010-12-21 at 18:28 +1100, Dave Chinner wrote: 
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > To use the generic percpu counter infrastructure for counters that
> > require conditional addition based on a threshold value we need
> > special handling of the counter. Further, the caller needs to know
> > the status of the conditional addition to determine what action to
> > take depending on whether the addition occurred or not.  Examples of
> > this sort of usage are resource counters that cannot go below zero
> > (e.g. filesystem free blocks).
> > 
> > To allow XFS to replace it's complex roll-your-own per-cpu
> > superblock counters, a single generic conditional function is
> > required: percpu_counter_add_unless_lt(). This will add the amount
> > to the counter unless the result would be less than the given
> > threshold. A caller supplied threshold is required because XFS does
> > not necessarily use the same threshold for every counter.
> > 
> > percpu_counter_add_unless_lt() attempts to minimise counter lock
> > traversals by only taking the counter lock when the threshold is
> > within the error range of the current counter value. Hence when the
> > threshold is not within the counter error range, the counter will
> > still have the same scalability characteristics as the normal
> > percpu_counter_add() function.
> > 
> > Adding this functionality to the generic percpu counters allows us
> > to remove the much more complex and less efficient XFS percpu
> > counter code (~700 lines of code) and replace it with generic
> > percpu counters.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> 
> I want to look at this one more closely again in the
> morning, but for now I'll just mention one nit, and
> one easily fixed problem.
> 
> 					-Alex
> 
> . . .
> 
> > + * Add @amount to @fdc if and only if result of addition is greater than or
>                      ^^^  should be fbc
> 
> > +EXPORT_SYMBOL(percpu_counter_add_unless_lt);
> > +
> 
> This has to be:
>     EXPORT_SYMBOL(__percpu_counter_add_unless_lt);
> (with leading underscores).

Yup, saw you comment about that on IRC overnight. Already fixed. ;)

Cheers,,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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  reply	other threads:[~2010-12-22  3:45 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-12-21  7:28 [PATCH 00/34] xfs: scalability patchset for 2.6.38 Dave Chinner
2010-12-21  7:28 ` [PATCH 01/34] xfs: provide a inode iolock lockdep class Dave Chinner
2010-12-21 15:15   ` Christoph Hellwig
2010-12-21  7:28 ` [PATCH 02/34] xfs: use KM_NOFS for allocations during attribute list operations Dave Chinner
2010-12-21 15:16   ` Christoph Hellwig
2010-12-21  7:28 ` [PATCH 03/34] lib: percpu counter add unless less than functionality Dave Chinner
2010-12-22  2:20   ` Alex Elder
2010-12-22  3:46     ` Dave Chinner [this message]
2010-12-21  7:29 ` [PATCH 04/34] xfs: use generic per-cpu counter infrastructure Dave Chinner
2010-12-21  7:29 ` [PATCH 05/34] xfs: demultiplex xfs_icsb_modify_counters() Dave Chinner
2010-12-21  7:29 ` [PATCH 06/34] xfs: dynamic speculative EOF preallocation Dave Chinner
2010-12-21 15:15   ` Christoph Hellwig
2010-12-21 21:42     ` Dave Chinner
2010-12-21 23:44       ` Dave Chinner
2010-12-22  2:29         ` Alex Elder
2010-12-29 12:56         ` Christoph Hellwig
2010-12-27 14:57   ` Alex Elder
2010-12-27 15:00   ` Alex Elder
2011-01-06 18:16   ` Christoph Hellwig
2010-12-21  7:29 ` [PATCH 07/34] xfs: don't truncate prealloc from frequently accessed inodes Dave Chinner
2010-12-21 16:45   ` Christoph Hellwig
2010-12-21  7:29 ` [PATCH 08/34] xfs: rcu free inodes Dave Chinner
2010-12-21  7:29 ` [PATCH 09/34] xfs: convert inode cache lookups to use RCU locking Dave Chinner
2010-12-21  7:29 ` [PATCH 10/34] xfs: convert pag_ici_lock to a spin lock Dave Chinner
2010-12-21  7:29 ` [PATCH 11/34] xfs: convert xfsbud shrinker to a per-buftarg shrinker Dave Chinner
2010-12-21  7:29 ` [PATCH 12/34] xfs: add a lru to the XFS buffer cache Dave Chinner
2010-12-21  7:29 ` [PATCH 13/34] xfs: connect up buffer reclaim priority hooks Dave Chinner
2010-12-21  7:29 ` [PATCH 14/34] xfs: fix EFI transaction cancellation Dave Chinner
2010-12-21  7:29 ` [PATCH 15/34] xfs: Pull EFI/EFD handling out from under the AIL lock Dave Chinner
2010-12-21  7:29 ` [PATCH 16/34] xfs: clean up xfs_ail_delete() Dave Chinner
2010-12-21  7:29 ` [PATCH 17/34] xfs: bulk AIL insertion during transaction commit Dave Chinner
2010-12-21  7:29 ` [PATCH 18/34] xfs: reduce the number of AIL push wakeups Dave Chinner
2010-12-21  7:29 ` [PATCH 19/34] xfs: consume iodone callback items on buffers as they are processed Dave Chinner
2010-12-21  7:29 ` [PATCH 20/34] xfs: remove all the inodes on a buffer from the AIL in bulk Dave Chinner
2010-12-22  2:20   ` Alex Elder
2010-12-22  3:49     ` Dave Chinner
2010-12-21  7:29 ` [PATCH 22/34] xfs: use AIL bulk delete function to implement single delete Dave Chinner
2010-12-21  7:29 ` [PATCH 23/34] xfs: convert log grant ticket queues to list heads Dave Chinner
2010-12-21  7:29 ` [PATCH 24/34] xfs: fact out common grant head/log tail verification code Dave Chinner
2010-12-21  7:29 ` [PATCH 25/34] xfs: rework log grant space calculations Dave Chinner
2010-12-21  7:29 ` [PATCH 26/34] xfs: combine grant heads into a single 64 bit integer Dave Chinner
2010-12-21  7:29 ` [PATCH 27/34] xfs: use wait queues directly for the log wait queues Dave Chinner
2010-12-21  7:29 ` [PATCH 28/34] xfs: make AIL tail pushing independent of the grant lock Dave Chinner
2010-12-21  7:29 ` [PATCH 29/34] xfs: convert l_last_sync_lsn to an atomic variable Dave Chinner
2010-12-21  7:29 ` [PATCH 30/34] xfs: convert l_tail_lsn " Dave Chinner
2010-12-29 12:52   ` Christoph Hellwig
2010-12-29 15:49   ` Alex Elder
2010-12-21  7:29 ` [PATCH 31/34] xfs: convert log grant heads to atomic variables Dave Chinner
2010-12-21  7:29 ` [PATCH 32/34] xfs: introduce new locks for the log grant ticket wait queues Dave Chinner
2010-12-21  7:29 ` [PATCH 33/34] xfs: convert grant head manipulations to lockless algorithm Dave Chinner
2010-12-21  7:29 ` [PATCH 34/34] xfs: kill useless spinlock_destroy macro Dave Chinner
2010-12-23  1:15 ` [PATCH 00/34] xfs: scalability patchset for 2.6.38 Dave Chinner

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