linux-kernel - Re: [patch 37/52] fs: icache lazy lru

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Date:	Thu, 1 Jul 2010 12:46:33 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	John Stultz <johnstul@...ibm.com>,
	Frank Mayhar <fmayhar@...gle.com>
Subject: Re: [patch 37/52] fs: icache lazy lru

On Wed, Jun 30, 2010 at 10:06:31PM +1000, Nick Piggin wrote:
> On Wed, Jun 30, 2010 at 06:38:14PM +1000, Dave Chinner wrote:
> > On Thu, Jun 24, 2010 at 01:02:49PM +1000, npiggin@...e.de wrote:
> > > Impelemnt lazy inode lru similarly to dcache. This will reduce lock
> > > acquisition and will help to improve lock ordering subsequently.
> > 
> > I'm not sure we want the I_REFERENCED reclaim free pass for a clean
> > inode that has been put on the LRU directly. I can see exactly how
> > it is benficial to delay reclaim of dirty inodes (XFS uses that
> > trick), but in terms of aging the cache we've already done this
> > free pass trick at the dentry level. Hence I think the frequent
> > separate access patterns tend to be filtered out at the dcache level
> > and hence we don't need to handle that in the inode cache.
> > 
> > Perhaps we only need the I_REFERENCED flag to give dirty inodes a
> > chance to be flushed by other means before forcing reclaim to do
> > inode writeback?
> 
> It doesn't force flush, but it force invalidates pagecache.

Sorry, bad choice of words - I should have said "forcing reclaim to
wait on inode writeback". That is what will happen in the case of
delayed allocation - the page cache will be clean, but the inode
can be dirty, so reclaiming such an inode would cause the shrinker
to block in clear_inode() waiting for inode writeback to
complete.

However, that is mostly irrelevant - you haven't comented at all on
whether the I_REFERENCED flag is too broad or even needed which is
what really needs to be discussed about this patch....

Cheers,

Dave.

-- 
Dave Chinner
david@...morbit.com
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