linux-kernel - Re: [PATCH 3/5] superblock: introduce per-sb cache shrinker infrastructure

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Message-ID: <20100527042453.GI22536@laptop>
Date:	Thu, 27 May 2010 14:24:53 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, xfs@....sgi.com
Subject: Re: [PATCH 3/5] superblock: introduce per-sb cache shrinker
 infrastructure

On Thu, May 27, 2010 at 02:07:04PM +1000, Dave Chinner wrote:
> On Thu, May 27, 2010 at 12:19:05PM +1000, Nick Piggin wrote:
> > On Thu, May 27, 2010 at 09:12:14AM +1000, Dave Chinner wrote:
> > > On Thu, May 27, 2010 at 02:41:16AM +1000, Nick Piggin wrote:
> > > > > +	count = ((sb->s_nr_dentry_unused + sb->s_nr_inodes_unused) / 100)
> > > > > +						* sysctl_vfs_cache_pressure;
> > > > 
> > > > Do you think truncating in the divisions is at all a problem? It
> > > > probably doesn't matter much I suppose.
> > > 
> > > Same code as currently exists. IIRC, the reasoning is that if we've
> > > got less that 100 objects to reclaim, then we're unlikely to be able
> > > to free up any memory from the caches, anyway.
> > 
> > Yeah, which is why I stop short of saying you should change it in
> > this patch.
> > 
> > But I think we should ensure things can get reclaimed eventually.
> > 100 objects could be 100 slabs, which could be anything from
> > half a meg to half a dozen. Multiplied by each of the caches.
> > Could be significant in small systems.
> 
> True, but usually there are busy objects in the dentry and inode
> slabs, so it shouldn't be a significant issue. We can probably
> address such problems if they can be demonstrated to be an issue in
> a separate patch set....

I didn't want to say it is a problem with your patchset, I just
thought of it when reviewing.
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