Re: The reason to call it 3.0 is the desktop (was Re: [OT] 2.6 not 3.0 - (NUMA))

[Lee Leahu]

Pardon my ignorance,

How does Readahead relate to journaling filesystems such as ReiserFS, or XFS?

Do they have the same or similar problems that I've been reading about with ext2/3?

Andrew Morton <[e-mail]> scribbled something about Re: The reason to call it 3.0 is the desktop (was Re: [OT] 2.6 not 3.0 -  (NUMA)):

> Daniel Phillips wrote:
> > 
> > On Sunday 06 October 2002 17:19, Martin J. Bligh wrote:
> > > > Then there's the issue of application startup. There's not enough
> > > > read ahead. This is especially sad, as the order of page faults is
> > > > at least partially predictable.
> > >
> > > Is the problem really, fundamentally a lack of readahead in the
> > > kernel? Or is it that your application is huge bloated pig?
> > 
> > Readahead isn't the only problem, but it is a huge problem.  The current
> > readahead model is per-inode, which is very little help with lots of small
> > files, especially if they are fragmented or out of order.  There are various
> > ways to fix this; they are all difficult[1].  Fortunately, we can call this
> > "tuning work" so it can be done during the stable series.
> > 
> > [1] We could teach each filesystem how to read ahead across directories, or
> > we could teach the vfs how to do physical readahead.  Choose your poison.
> 
> Devices do physical readahead, and it works nicely.
> 
> Go into ext2_new_inode, replace the call to find_group_dir with
> find_group_other.  Then untar a kernel tree, unmount the fs,
> remount it and see how long it takes to do a
> 
> 	`find . -type f  xargs cat > /dev/null'
> 
> on that tree.  If your disk is like my disk, you will achieve
> full disk bandwidth.
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