linux-kernel - Re: inodes: Support generic defragmentation

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Message-ID: <20100131083409.GF29555@one.firstfloor.org>
Date:	Sun, 31 Jan 2010 09:34:09 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	tytso@....edu, Christoph Lameter <cl@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Chinner <david@...morbit.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	Alexander Viro <viro@....linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Christoph Lameter <clameter@....com>,
	Rik van Riel <riel@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	akpm@...ux-foundation.org, Nick Piggin <nickpiggin@...oo.com.au>,
	Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org
Subject: Re: inodes: Support generic defragmentation

On Sat, Jan 30, 2010 at 02:26:23PM -0500, tytso@....edu wrote:
> On Fri, Jan 29, 2010 at 02:49:42PM -0600, Christoph Lameter wrote:
> > This implements the ability to remove inodes in a particular slab
> > from inode caches. In order to remove an inode we may have to write out
> > the pages of an inode, the inode itself and remove the dentries referring
> > to the node.
> 
> How often is this going to happen?  Removing an inode is an incredibly

The standard case is the classic updatedb. Lots of dentries/inodes cached
with no or little corresponding data cache.

> a huge number of pages that are actively getting used, the thrashing
> that is going to result is going to enormous.

I think the consensus so far is to try to avoid any inodes/dentries
which are dirty or used in any way.

I personally would prefer it to be more aggressive for memory offlining
though for RAS purposes though, but just handling the unused cases is a 
good first step.

> "invalidate_mapping_pages() will not block on I/O activity, and it
> will refuse to invalidate pages which are dirty, locked, under
> writeback, or mapped into page tables."

I think that was the point.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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