Messages in this thread |  | | | Date | Thu, 2 Apr 2009 19:19:58 -0700 | | Subject | Re: EXT4-ish "fixes" in UBIFS | | From | David Rees <> |
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On Thu, Apr 2, 2009 at 7:05 PM, Trenton D. Adams <trenton.d.adams@gmail.com> wrote: > On Thu, Apr 2, 2009 at 7:55 PM, David Rees <drees76@gmail.com> wrote: >> On Thu, Apr 2, 2009 at 5:28 PM, Trenton D. Adams >> <trenton.d.adams@gmail.com> wrote: >>> Oh, I should have clarified. It improves performance under heavy >>> load. Under normal load, mounting without sync is fine. What I tend >>> to do is mount with "remount,rw,sync" when heavy load is starting. >>> Then my system goes slowly, but latency is good. Then, when it's all >>> done (say a big compile, or job, or whatever), I remount without sync >>> again. >>> >>> I'm thinking of writing a script that monitors performance, and >>> remounts as needed, lol. WHAT A HACK. hehe. >> >> All you're doing here is implementing the lowering of dirty data >> limits in the VM dynamically based on how long fsyncs take. >> >> Linus outlined this specific strategy as "the ideal siutation" >> somewhere in the depths of "That filesystem thread". > > I thought he said it was a HORRIBLE solution. :D I recall him > slamming Andrew over it. Unless you're referring to the kernel > actually doing it on the fly.
Yes - you are correct - doing it in userspace isn't the best place to put it - but if you can do it there, the same ideas could then be pushed into the kernel and further enhanced.
>> Look at the new in 2.6.29 dirty*bytes parameters in >> Documentation/sysctl/vm.txt for more info. By lowering those values, >> you can effectively turn normal writes into synchronous writes which >> will greatly reduce latency of fsync under heavy write load. >> >> In previous kernels you can tweak dirty_ratio and >> dirty_background_ratio, but they don't have the granularity of the new >> knobs. Although if you are talking about just remounting in sync >> mode, they may work for you at least as a proof of concept. ;-) > > dirty_ratio and dirty_background never really had any affect for me. > I'll look into the other parameters. Waiting for the checkout again, > as I am currently under a heavy rsync load (*rolls eyes*).
How low have you set them? Try setting them to 2 and 1 respectively. It cuts down fsync latencies by a significant amount in my experience.
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