Re: Performance of ext4

[Holger Kiehl]

On Wed, 11 Jun 2008, Aneesh Kumar K.V wrote:

> On Wed, Jun 11, 2008 at 08:02:32AM +0000, Holger Kiehl wrote:
> > 2 years ago I used 2.6.16.8 but the hardware is still the same. So what has
> > happened with the performance of ext4? I noticed that 2 years ago I could
> > use extents+mballoc+delalloc, now there is only extents+mballoc in the
> > current kernels. Could delalloc make the big difference? I saw that
> > in Andrew Morton mm tree delalloc is included. Unfortunately when I tried using
> > 2.6.26-rc2-mm1 a sync would never return and there where lot of other
> > odd things, so I could not do any tests with delalloc.
>
>
> The sync and other related hangs should be fix with the latest patches
> vailable at http://repo.or.cz/w/ext4-patch-queue.git. Using mballoc have
> an impact on CPU utilization because we try to build an in-memory extent
> map of free blocks available in the group. The cold cache run (the first
> run) would take more time because of the time needed to build the extent
> map. So repeating the same test and looking at the numbers would help us
> understand the impact of in-memory extent building code.
Not sure if I understand this. I first formated the file system and run the
test three times.

> > So any idea what I am doing wrong or what I could do to improve those numbers?
> > Please CC me since I am not subscribed to the list.
>
> You should be able to apply the patches in the patchqueue mentioned above  to 2.6.26-rc5
> Can you test with the same and get the numbers. ? Also delalloc enabled
> by default with changes from patchqueue force writeback mode for
> journal. So you may want to enable writeback for ext3.
Against a clean 2.6.26-rc5 the patchqueue does not apply. Lots of rejects.
The patchqueue also contains changes for defrag that are not in 2.6.26-rc5.
Or did you mean to apply those against the mm tree?

Thanks,
Holger

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