mmap over nfs leads to excessive system load

[Kenny Simpson]

I seem to have hit the same issue as Fabio Brugnara
http://www.ussg.iu.edu/hypermail/linux/kernel/0505.0/1061.html
but although he said the problem went away for him in 2.6.11, I saw the problem
in 2.6.8, and still see it in 2.6.14.

When using a sliding mmap window over a file on nfs, the system time increases
with time, and the throughput drops.
Using the same program on a local file I get about 30MB/s with very little
system time... just a bunch of iowait.

I am using a gigabit connection to a netapp, and initially get 30+MB/s, but
after about 30 seconds, this decays to only about 8MB/s with the system time
close to 80%.

I did a quick Oprofile run, and here is the top of the list:

1739810  16.8926  vmlinux-2.6.14           vmlinux-2.6.14          
find_get_pages_tag
1305104  12.6718  vmlinux-2.6.14           vmlinux-2.6.14          
mpage_writepages
1041147  10.1089  vmlinux-2.6.14           vmlinux-2.6.14           unlock_page
998692    9.6967  vmlinux-2.6.14           vmlinux-2.6.14          
clear_page_dirty_for_io
966458    9.3838  vmlinux-2.6.14           vmlinux-2.6.14          
release_pages
674434    6.5484  vmlinux-2.6.14           vmlinux-2.6.14          
pci_conf1_write
486345    4.7221  vmlinux-2.6.14           vmlinux-2.6.14          
__lookup_tag
399627    3.8801  vmlinux-2.6.14           vmlinux-2.6.14          
page_waitqueue
134250    1.3035  vmlinux-2.6.14           vmlinux-2.6.14          
_spin_lock_irqsave
130594    1.2680  vmlinux-2.6.14           vmlinux-2.6.14          
_read_lock_irqsave


I'm attaching the config.
Other details:
  Dual Xeon 2.66 w/ 2GB RAM
  Debian sarge + 2.6.14 kernel + glibc 2.3.5
  nvidia drivers
  broadcom gigabit driver (8.2.18)

thanks,
-Kenny


		
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Attachment: config-2.6.14
Description: 1636389412-config-2.6.14