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Re: [patch 01/12] xfs: split tail_lsn assignments from log space wakeups

To: Ben Myers <bpm@xxxxxxx>
Subject: Re: [patch 01/12] xfs: split tail_lsn assignments from log space wakeups
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Fri, 17 Feb 2012 14:21:12 -0500
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20120216182121.GQ7762@xxxxxxx>
References: <20111212141346.986825692@xxxxxxxxxxxxxxxxxxxxxx> <20111212141433.542846138@xxxxxxxxxxxxxxxxxxxxxx> <20120216182121.GQ7762@xxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
> >     if (!list_empty(&tmp))
> >             xfs_ail_splice(ailp, cur, &tmp, lsn);
> > +   spin_unlock(&ailp->xa_lock);
> 
> Right.  I am uncomfortable with the idea of dropping the ail lock here
> and then retaking it below in xlog_assign_tail_lsn.  Your suggestion
> that a variant of xlog_assign_tail_lsn which expects the lock to be held
> seems reasonable.

There is no risk in dropping it in terms of correctness, the only
downside is doupling the amount of lock roundtrips.  The reason why
I didn't do the version that is called with the lock held is that it
would be fairly intrusive and ugly.

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