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Re: [PATCH 1/5] inode: Make unused inode LRU per superblock

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 1/5] inode: Make unused inode LRU per superblock
From: Nick Piggin <npiggin@xxxxxxx>
Date: Fri, 28 May 2010 20:07:19 +1000
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20100527225418.GP12087@dastard>
References: <1274777588-21494-1-git-send-email-david@xxxxxxxxxxxxx> <1274777588-21494-2-git-send-email-david@xxxxxxxxxxxxx> <20100527133230.780be6c7.akpm@xxxxxxxxxxxxxxxxxxxx> <20100527225418.GP12087@dastard>
User-agent: Mutt/1.5.20 (2009-06-14)
On Fri, May 28, 2010 at 08:54:18AM +1000, Dave Chinner wrote:
> On Thu, May 27, 2010 at 01:32:30PM -0700, Andrew Morton wrote:
> > On Tue, 25 May 2010 18:53:04 +1000
> > Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> > 
> > > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > > 
> > > The inode unused list is currently a global LRU. This does not match
> > > the other global filesystem cache - the dentry cache - which uses
> > > per-superblock LRU lists. Hence we have related filesystem object
> > > types using different LRU reclaimatin schemes.
> > > 
> > > To enable a per-superblock filesystem cache shrinker, both of these
> > > caches need to have per-sb unused object LRU lists. Hence this patch
> > > converts the global inode LRU to per-sb LRUs.
> > > 
> > > The patch only does rudimentary per-sb propotioning in the shrinker
> > > infrastructure, as this gets removed when the per-sb shrinker
> > > callouts are introduced later on.
> > > 
> > > ...
> > >
> > > +                 list_move(&inode->i_list, &inode->i_sb->s_inode_lru);
> > 
> > It's a shape that s_inode_lru is still protected by inode_lock.  One
> > day we're going to get in trouble over that lock.  Migrating to a
> > per-sb lock would be logical and might help.
> > 
> > Did you look into this? 
> 
> Yes, I have. Yes, it's possible.  It's solving a different problem,
> so I figured it can be done in a different patch set.

It almost all goes away in my inode lock splitup patches. Inode lru
and dirty lists were the last things protected by the global lock
there.

I am actually going to do per-zone lrus for these guys and per-zone
locks (which is actually better than per-sb because it gives NUMA
scalability within a single sb).

The dirty/writeback lists should probably be per-bdi locked.


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