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From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>, Nick Piggin <npiggin@suse.de>
Cc: xfs@oss.sgi.com
Subject: Re: [PATCH 5/6] [XFS] Replace per-ag array with a radix tree
Date: Fri, 11 Dec 2009 06:46:27 -0500	[thread overview]
Message-ID: <20091211114627.GB5436@infradead.org> (raw)
In-Reply-To: <20091211004353.GF30608@discord.disaster>

On Fri, Dec 11, 2009 at 11:43:53AM +1100, Dave Chinner wrote:
> > > +	spin_lock(&mp->m_perag_lock);
> > > +	pag = radix_tree_lookup(&mp->m_perag_tree, agno);
> > > +	spin_unlock(&mp->m_perag_lock);
> > > +	return pag;
> > 
> > Can't we do this as a lock-less (at least for lookups) radix tree?
> 
> I think it can be (RCU-based?) , but I think that makes sense as a
> followup optimisation once we have confidence the code is working
> as it should.

Nick, what are the rules for the lock-less radix tree reader side?

Dave is introducing a radix tree in XFS which has the following access
pattern:

 - lots of read side access during normal fs operations
 - insertations currently only happen during mount before the fs is life
   and during a very rare operation (filesystem resize)
 - currently items are never deleted, but we might need that in the
   future (for filesystem shrink support)
 - the objects pointed to are kmalloced and refcounted structures,
   but we don't even strictly need the refcounting until the filesystem
   shrink support is implemented

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  parent reply	other threads:[~2009-12-11 11:45 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-12-02  6:11 [PATCH 0/6] [XFS] Fix growfs deadlocks and per-AG use after free Dave Chinner
2009-12-02  6:11 ` [PATCH 1/6] [XFS] rename xfs_get_perag Dave Chinner
2009-12-10 23:15   ` Christoph Hellwig
2009-12-10 23:25     ` Dave Chinner
2009-12-02  6:11 ` [PATCH 2/6] [XFS] Don't directly reference m_perag in allocation code Dave Chinner
2009-12-10 23:18   ` Christoph Hellwig
2009-12-10 23:41     ` Dave Chinner
2009-12-02  6:11 ` [PATCH 3/6] [XFS] Convert filestreams code to use per-ag get/put routines Dave Chinner
2009-12-10 23:22   ` Christoph Hellwig
2009-12-02  6:11 ` [PATCH 4/6] [XFS] convert remaining direct references to m_perag Dave Chinner
2009-12-10 23:24   ` Christoph Hellwig
2009-12-02  6:11 ` [PATCH 5/6] [XFS] Replace per-ag array with a radix tree Dave Chinner
2009-12-10 23:45   ` Christoph Hellwig
2009-12-11  0:43     ` Dave Chinner
2009-12-11 11:43       ` Christoph Hellwig
2009-12-11 11:46       ` Christoph Hellwig [this message]
2009-12-14  4:16         ` Nick Piggin
2009-12-02  6:11 ` [PATCH 6/6] [XFS] Reference count per-ag structures Dave Chinner
2009-12-10 23:48   ` Christoph Hellwig
2009-12-11  0:50     ` Dave Chinner
  -- strict thread matches above, loose matches on Subject: below --
2009-12-14 23:11 [PATCH 0/6] XFS: Fix growfs deadlocks and per-AG use after free V2 Dave Chinner
2009-12-14 23:11 ` [PATCH 5/6] XFS: Replace per-ag array with a radix tree Dave Chinner
2009-12-15  6:11 [PATCH 0/6] XFS: Fix growfs deadlocks and per-AG use after free V3 Dave Chinner
2009-12-15  6:11 ` [PATCH 5/6] XFS: Replace per-ag array with a radix tree Dave Chinner
2009-12-23 16:02   ` Christoph Hellwig
2009-12-23 22:08   ` Alex Elder
2009-12-26  4:17     ` Dave Chinner

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