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SubjectRe: pdflush eating a lot of CPU on heavy NFS I/O
On Tue, 27 Apr 2004, Andrew Morton wrote:

> Brent Cook <busterbcook@yahoo.com> wrote:
> >
> > Running any kernel from the 2.6.6-rc* series (and a few previous
> > -mm*'s),
>
> It's a shame this wasn't reported earlier.

Since it was a pretty big deal on my system, I just assumed it was for
other people's too, and that someone else would have reported it by
now. I only got concerned when it persisted between rc's.

> > the pdflush process starts using near 100% CPU indefinitely after
> > a few minutes of initial NFS traffic, as far as I can tell.
>
> Please confirm that the problem is observed on the NFS client and not the
> NFS server? I'll assume the client.

Yes, both affected machines had the issue when connecting as a client to a
2.4.25-based NFS server.

> What other filesystems are in use on the client?

One uses Reiser on /, the other uses ext3 on /. Here is the mount table
for one machine:

/dev/hda3 on / type ext3 (rw)
none on /dev/pts type devpts (rw,gid=5,mode=620)
none on /proc type proc (rw)
none on /sys type sysfs (rw)
usbfs on /proc/bus/usb type usbfs (rw)
ozma:/home on /home type nfs (rw,addr=192.168.1.1)

Running 2.6.6-rc2-mm1,
Here is a shot compiling KDE with the source on the NFS mount,
-j2. This is the initial state:

PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME CPU COMMAND
12091 busterb 25 0 63524 59M 5140 R 38.4 23.8 0:19 0 cc1plus
12199 busterb 25 0 55660 52M 5140 R 38.0 20.8 0:07 0 cc1plus
7 root 16 0 0 0 0 SW 4.9 0.0 0:03 0 pdflush

About 10 minutes into the process, pdflush starts taking over:

PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME CPU COMMAND
7 root 25 0 0 0 0 RW 34.4 0.0 3:05 0 pdflush
17856 busterb 25 0 69400 65M 5140 R 34.4 26.1 0:31 0 cc1plus
19466 busterb 25 0 43732 39M 5140 R 26.3 15.5 0:03 0 cc1plus

After stopping the compile, pdflush remains until a reboot:

PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME CPU COMMAND
7 root 25 0 0 0 0 RW 98.0 0.0 3:21 0 pdflush

The network light will flash continually on each machine once pdflush
gets into this state, which makes me think NFS. Each machine has
512-256 MB of ram and a single CPU.

- Brent
-
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