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    SubjectRe: [PATCH 00/23] per device dirty throttling -v8

    On Sat, 4 Aug 2007, Ingo Molnar wrote:
    > yeah, it's really ugly. But otherwise i've got no real complaint about
    > ext3 - with the obligatory qualification that "noatime,nodiratime" in
    > /etc/fstab is a must.

    I agree, we really should do something about atime.

    But the fsync thing is a real issue. It literally makes ext3 almost
    unusable from a latency standpoint on many loads. I have a fast disk, and
    don't actually tend to have all that much going on normally, and it still
    hurts occasionally.

    One of the most common (and *best*) reasons for using fsync is for the
    mail spool. So anybody that uses local email will actually be doing a lot
    of fsync, and while you could try to thread the interfaces, I don't think
    a lot of mailers do.

    So fsync ends up being a latency issue for something that a lot of people
    actually see, and something that you actually end up working with and you
    notice the latencies very clearly. Your editor auto-save feature is
    another good example of that exact same thing: the fsync actually is there
    for a very good reason, even if you apparently decided that you'd rather
    disable it.

    But yeah, "noatime,data=writeback" will quite likely be *quite* noticeable
    (with different effects for different loads), but almost nobody actually
    runs that way.

    I ended up using O_NOATIME for the individual object "open()" calls inside
    git, and it was an absolutely huge time-saver for the case of not having
    "noatime" in the mount options. Certainly more than your estimated 10%
    under some loads.

    The "relatime" thing that David mentioned might well be very useful, but
    it's probably even less used than "noatime" is. And sadly, I don't really
    see that changing (unless we were to actually change the defaults inside
    the kernel).

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      Last update: 2007-08-04 19:43    [W:0.026 / U:3.196 seconds]
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