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An unexpected perf feature
LWN.net Weekly Edition for May 16, 2013
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LWN.net Weekly Edition for May 9, 2013
Wow, this is a massive improvement!
Flushing out pdflush
Posted Apr 4, 2009 20:59 UTC (Sat) by nix (subscriber, #2304)
Posted Apr 5, 2009 0:09 UTC (Sun) by knobunc (subscriber, #4678)
Posted Apr 5, 2009 11:56 UTC (Sun) by nix (subscriber, #2304)
A thread pool would surely be better (for something like this, anyway, in
which the full complement will only be needed in extreme situations).
There are several thread pools in the kernel (pdflush) or out-of-tree
patches (fs-cache's slow-work threads) already. It's quite doable.
Posted Apr 5, 2009 14:27 UTC (Sun) by i3839 (guest, #31386)
A thread pool would only be better if you would otherwise allocate too many threads per device. But if you allocated too many, there's nothing that prevents having a too high number of threads in the pool either, so it's just shuffling the problem around.
Posted Apr 5, 2009 18:27 UTC (Sun) by nix (subscriber, #2304)
Posted Apr 6, 2009 11:44 UTC (Mon) by i3839 (guest, #31386)
Posted Apr 6, 2009 19:31 UTC (Mon) by nix (subscriber, #2304)
Posted Apr 17, 2009 12:41 UTC (Fri) by axboe (subscriber, #904)
It's mostly to satisfy the people getting annoyed when looking at the ps output. An idle kernel thread is essentially free. Of course if you have 10000 logical disks in your system, you'll probably appreciate not spending memory on the threads at least.
Posted Apr 17, 2009 22:29 UTC (Fri) by nix (subscriber, #2304)
(Also, kernel threads still need a kernel stack: that's 8Kb of memory you
won't see again. Not much by modern standard perhaps...)
Posted Apr 17, 2009 23:43 UTC (Fri) by njs (guest, #40338)
But anyway, yeah, for ordinary systems the memory usage matters a little but not much.
Posted Apr 7, 2009 20:08 UTC (Tue) by jzbiciak (✭ supporter ✭, #5246)
At a given point of time, there are between two and eight pdflush threads running in the system.
With a ten-disk btrfs filesystem, per-BDI flushing performed 25% faster
Posted Apr 17, 2009 12:39 UTC (Fri) by axboe (subscriber, #904)
Posted Feb 10, 2011 8:25 UTC (Thu) by bergwolf (subscriber, #55931)
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