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Re: [PATCH 1/7] xfs: use a normal shrinker for the dquot freelist

To: Ben Myers <bpm@xxxxxxx>
Subject: Re: [PATCH 1/7] xfs: use a normal shrinker for the dquot freelist
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 10 Feb 2012 12:52:33 +1100
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20120209231346.GM7762@xxxxxxx>
References: <20120201135719.202171828@xxxxxxxxxxxxxxxxxxxxxx> <20120201140039.011990931@xxxxxxxxxxxxxxxxxxxxxx> <20120209220320.GL7762@xxxxxxx> <20120209225626.GA844@xxxxxxxxxxxxx> <20120209231346.GM7762@xxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Feb 09, 2012 at 05:13:46PM -0600, Ben Myers wrote:
> On Thu, Feb 09, 2012 at 05:56:26PM -0500, Christoph Hellwig wrote:
> > On Thu, Feb 09, 2012 at 04:03:20PM -0600, Ben Myers wrote:
> > > > -
> > > > -       return B_TRUE;
> > > > +       while (!list_empty(&dispose_list)) {
> > > > +               dqp = list_first_entry(&dispose_list, struct xfs_dquot,
> > > > +                                      q_freelist);
> > > > +               list_del_init(&dqp->q_freelist);
> > > > +               xfs_qm_dqfree_one(dqp);
> > > > +       }
> > > > +out:
> > > > +       return (xfs_Gqm->qm_dqfrlist_cnt / 100) * 
> > > > sysctl_vfs_cache_pressure;
> > > 
> > > return atomic_read(&xfs_Gqm->qm_totaldquots);
> > > 
> > > This works well for me and seems to be closer to the shrinker interface
> > > as documented:
> > 
> > It's pointless - we can only apply pressure to dquots that are on the
> > freelist.  No amount of shaking will allow us to reclaim a referenced
> > dquot.
> 
> Sure... then it should be:
> 
> return atomic_read(&xfs_Gqm->qm_frlist_cnt);
> 
> What is the value of the additional calculation?

It's applying the user controllable vfs_cache_pressure setting to
the reclaim weight. That is, if the user wants to reclaim
inode/dentry/dquot slab caches faster than the page cache (i.e.
perfer data caching over metadata caching) or vice cersa, then the
change the sysctl value and shrinkers should then take that into
account....

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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