temporarily system freeze with high I/O write to ext2 fs

temporarily system freeze with high I/O write to ext2 fs

[Roy Sigurd Karlsbakk]

hi all

why is it that Linux 'hangs' while doing heavy I/O operations (such as dd)
to (and perhaps from?) ext2 file systems? I can't see the same behaivour
when using other file systems, such as ReiserFS

roy

--
Roy Sigurd Karlsbakk, MCSE, MCNE, CLS, LCA

Computers are like air conditioners.
They stop working when you open Windows.

Re: temporarily system freeze with high I/O write to ext2 fs

[Andrew Morton]

Roy Sigurd Karlsbakk wrote:
> 
> hi all
> 
> why is it that Linux 'hangs' while doing heavy I/O operations (such as dd)
> to (and perhaps from?) ext2 file systems? I can't see the same behaivour
> when using other file systems, such as ReiserFS
> 

A partial fix for this went into 2.4.17-pre2.  What kernel are you
using?

For how long does it "hang"?   What exactly are you doing when it
occurs?

Is your disk system well-tuned?  What throughput do you get with
`hdparm -t /dev/hdXX'?

It surprises me that resierfs behaves differently...

-

Re: temporarily system freeze with high I/O write to ext2 fs

[James Stevenson]

> > why is it that Linux 'hangs' while doing heavy I/O operations (such as
dd)
> > to (and perhaps from?) ext2 file systems? I can't see the same behaivour
> > when using other file systems, such as ReiserFS
> >
>
> A partial fix for this went into 2.4.17-pre2.  What kernel are you
> using?

i have always had with problem normally during disk writes.
currently on 2.4.x-14 + 2.4.16

> For how long does it "hang"?   What exactly are you doing when it
> occurs?

its not that it hangs but it gets extremely laggy eg 2/3 seconds pause
for keyboard input to appear on a console.

> Is your disk system well-tuned?  What throughput do you get with
> `hdparm -t /dev/hdXX'?

i have tuned with hdparm as much as i can. but i cannot tune the
VM because the files in /proc/sys/vm do not seem to make any difference
to the system at all and the documents dont seem to be correct inn
procfs.txt
if docs are wrong for a kernel version would it not be better to either say
they are wrong
or remove them alll together. but i assume this is todo with the latest VM
change.

are there going to be new documents for these files ?

    James

Re: temporarily system freeze with high I/O write to ext2 fs

[Andrew Morton]

James Stevenson wrote:
> 
> > > why is it that Linux 'hangs' while doing heavy I/O operations (such as
> dd)
> > > to (and perhaps from?) ext2 file systems? I can't see the same behaivour
> > > when using other file systems, such as ReiserFS
> > >
> >
> > A partial fix for this went into 2.4.17-pre2.  What kernel are you
> > using?
> 
> i have always had with problem normally during disk writes.
> currently on 2.4.x-14 + 2.4.16

Please try 2.4.17-pre2 or later.

> > For how long does it "hang"?   What exactly are you doing when it
> > occurs?
> 
> its not that it hangs but it gets extremely laggy eg 2/3 seconds pause
> for keyboard input to appear on a console.

Your app got paged out, and the enormous read latencies in 2.4.16
caused it to remain there.

Re: temporarily system freeze with high I/O write to ext2 fs

[James Stevenson]

> >
> > > > why is it that Linux 'hangs' while doing heavy I/O operations (such
as
> > dd)
> > > > to (and perhaps from?) ext2 file systems? I can't see the same
behaivour
> > > > when using other file systems, such as ReiserFS
> > > >
> > >
> > > A partial fix for this went into 2.4.17-pre2.  What kernel are you
> > > using?
> >
> > i have always had with problem normally during disk writes.
> > currently on 2.4.x-14 + 2.4.16
>
> Please try 2.4.17-pre2 or later.
>

ok i should have some time to try that at the weekend.

> > its not that it hangs but it gets extremely laggy eg 2/3 seconds pause
> > for keyboard input to appear on a console.
>
> Your app got paged out, and the enormous read latencies in 2.4.16
> caused it to remain there.

why would it have been paged out there was loads of free
ram. there is 192MB in the machine and no X windows or
anything and the app was bash and there are not many other processes.

    James