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

Lee Leahu
2002-10-30T18:19:49Z

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 <akpm@digeo.com> 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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