[Bug 131094] Re: Heavy Disk I/O harms desktop responsiveness

[Jim Lieb]

This regression has been around since about the 2.6.18 timeframe and has
eluded a lot of testing to isolate the root cause.  The most promising
fix is in the VM subsystem (mm) where the LRU scan has been changed to
favor keeping executable pages active longer.  Most of these symptoms
come down to VM thrashing to make room for I/O pages.  The key
change/commit is ab4754d24a0f2e05920170c845bd84472814c6, "vmscan: make
mapped executable pages the first class citizen".  For those interested
in the details and are familiar with 'git', the commit changelog entry
has a complete description of the problem and the fix.  You can find
this in either the ubuntu-karmic git repository or on kernel.org.

This change was merged into the 2.6.31r1 kernel.  The Karmic Alpha 3
snapshot, currently scheduled for the last week of July, will have a
2.6.31 kernel containing this change.  Please test this version and
report back whether your latency issues have been resolved.  There is no
guarantee that this change will solve the latency problems in any
particular workload so as much testing in a variety of machines and
workloads is important.

Thank you.

NOTE: This new version of the Karmic kernel will also have the new KMS
patches to match the upgrade of the Xorg server.  Since most of the
latency complaints center around GUI latencies, this adds a new set of
variables.  There are mainline kernel packages available now for those
who cannot wait for the Alpha 3 release that can run on either Jaunty or
Karmic (alpha) but they may have problems with the older Xorg server.
If you find X related problems with these kernels, please wait for the
Alpha 3 release and not bother to report X problems unless they are also
present in the A3 release.

Backporting note:
The commit mentioned above is just one change in the VM subsystem.  Backporting this and the number of its associated patches back to a Jaunty (2.6.28) or earlier kernels would probably not be productive and may create new stability problems of their own given the amount of change between the two versions.

** Changed in: linux (Ubuntu)
       Status: Confirmed => In Progress

** Changed in: linux (Ubuntu)
     Assignee: (unassigned) => Jim Lieb (lieb)

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Heavy Disk I/O harms desktop responsiveness
https://bugs.launchpad.net/bugs/131094
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