Messages in this thread |  | | From | Neil Brown <> | Date | Fri, 2 Feb 2007 17:41:33 +1100 | Subject | Re: [RFC 0/8] Cpuset aware writeback |
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On Thursday February 1, clameter@sgi.com wrote: > > > The network stack is of course a different (much harder) problem. > > An NFS solution is possible without solving the network stack issue?
NFS is currently able to make more than max_dirty_ratio of memory Dirty/Writeback without being effectively throttled. So it can use up way more than it should and put pressure in the network stack.
If NFS were throttled like other block-based filesystems (which Peter's patch should do), then there will normally be a lot more head room and the network stack will normally be able to cope. There might still be situations were you can run out of memory to the extent that NFS cannot make forward progress, but they will be substantially less likely (I think you need lots of TCP streams with slow consumers and fast producers so that TCP is forced to use up it reserves).
The block layer guarantees not to run out of memory. The network layer makes a best effort as long as nothing goes crazy. NFS (currently) doesn't do quite enough to stop things going crazy.
At least, that is my understanding.
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