Re: A unresponsive file system can hang all I/O in the system on linux-2.6.23-rc6 (dirty_thresh problem?)

From: Chakri n
Date: Fri Sep 28 2007 - 04:27:30 EST


The BDI dirty limits sounds like a good idea.

Is there already a patch for this, which I could try?

I believe it works like this,

Each BDI, will have a limit. If the dirty_thresh exceeds the limit,
all the I/O on the block device will be synchronous.

so, if I have sda & a NFS mount, the dirty limit can be different for
each of them.

I can set dirty limit for
- sda to be 90% and
- NFS mount to be 50%.

So, if the dirty limit is greater than 50%, NFS does synchronously,
but sda can work asynchronously, till dirty limit reaches 90%.


On 9/27/07, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> On Thu, 2007-09-27 at 23:50 -0700, Andrew Morton wrote:
> > What we _don't_ want to happen is for other processes which are writing to
> > other, non-dead devices to get collaterally blocked. We have patches which
> > might fix that queued for 2.6.24. Peter?
> Nasty problem, don't do that :-)
> But yeah, with per BDI dirty limits we get stuck at whatever ratio that
> NFS server/mount (?) has - which could be 100%. Other processes will
> then work almost synchronously against their BDIs but it should work.
> [ They will lower the NFS-BDI's ratio, but some fancy clipping code will
> limit the other BDIs their dirty limit to not exceed the total limit.
> And with all these NFS pages stuck, that will still be nothing. ]
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