Re: Re: [RFC] ext3 writepages for writeback mode

[Sonny Rao <sonny@burdell.org>]

On Fri, Feb 11, 2005 at 04:09:46PM -0800, Badari Pulavarty wrote:
> On Fri, 2005-02-11 at 15:58, Andrew Morton wrote:
> > Badari Pulavarty <pbadari@us.ibm.com> wrote:
> > >
> > > Due to lack of interesting suggestions to solve 
> > > mpage_writepages() -> ext3_writeback_writepage() problem,
> > > I fixed it in the dumbest possible way.
> > 
> > I've actually forgotten what the problem was.  It was 100 patches ago :(
> 
> The problem was 
> 	ext3_writeback_writepages() -> mpage_writepages() could
> call back ext3_writeback_writepage() in the "confused" case.
> ext3_writeback_writepage() could end up doing nothing, since the
> we already have a journal handle.
> 
> I added a writepage_helper to handle this case.
> 
> > 
> > > Let me know, what you think.
> > 
> > 
> > If it works, let's get some benchmark numbers so we can decide whether it
> > justifies more development?
> > 
> 
> Yep. I will get some numbers to see ..
> 

I'm helping Badari collecting data on this...

My setup is a P4 2.0Ghz booted with 1GB of RAM and 1 cpu attached via
Fiber to a seven disk raid0 array with write-caching turned off
(write-cacheing can skew numbers significantly if you aren't careful
to let the cache drain between runs, etc.) 

The test is a single-threaded sequential overwrite of a 20GB data set
divided into 512MB files which are selected randomly and overwritten.

All of these numbers represent the average of three five-minute runs.

All ext3 tests are in writeback mode

FS		Throughput	Cpu Utilizaiton
--		----------	---------------
Ext3		78 MB/sec	75.9 %
Ext3 + wpages	85 MB/sec	74.7 %

Just for comparison:

Ext2		88.5 MB/sec	74.2 %
Ext2 + nobh	89.6 MB/sec	71.7 %

JFS		94.8 MB/sec	85.6 %
XFS		100 MB/sec	95.5 %


So, Badari's writepages patch improves performance on this particular
setup by almost 10 %


I can rerun with more processors/ram, or different disk configurations
if anyone is interested.

Sonny


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