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    SubjectRe: EXT4-ish "fixes" in UBIFS
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    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:
    >> On Thu, Apr 2, 2009 at 6:24 PM, Trenton D. Adams
    >> <trenton.d.adams@gmail.com> wrote:
    >>> Yes, mounting "-o sync" does improve ext3 performance.  It sucks
    >>> though, because I do want quick writes.  And mounting with sync option
    >>> slows down to disk io speeds.  In my case, that's between 20 and 23
    >>> megabytes per second *big frown, quivering lip, and tears in my eyes*.
    >>> :P
    >>>
    >>
    >> 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.

    >
    > 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. ;-)
    >
    > -Dave
    >

    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*).

    Thanks.
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