Re: EXT4-ish "fixes" in UBIFS

[David Rees]

On Thu, Apr 2, 2009 at 7:28 PM, Trenton D. Adams
<trenton.d.adams@xxxxxxxxx> wrote:
> On Thu, Apr 2, 2009 at 8:19 PM, David Rees <drees76@xxxxxxxxx> wrote:
>> On Thu, Apr 2, 2009 at 7:05 PM, Trenton D. Adams <trenton.d.adams@xxxxxxxxx> wrote:
>>> On Thu, Apr 2, 2009 at 7:55 PM, David Rees <drees76@xxxxxxxxx> wrote:
>>>> On Thu, Apr 2, 2009 at 5:28 PM, Trenton D. Adams <trenton.d.adams@xxxxxxxxx> wrote:
>>> 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.
>
> That's the odd thing, I was setting them to 2 and 1.  I was just
> looking at the 2.6.29 code, and it should have made a difference.  I
> don't know what version of the kernel I was using at the time.  And,
> I'm not sure if I had the 1M fsync tests in place at the time either,
> to be sure about what I was testing.  It could be that I wasn't being
> very scientific about it at the time.  Thanks though, that setting
> makes a huge difference.

Well, it depends on how much memory you have.  Keep in mind that those
are percentages - so if you have 2GB RAM, that's the same as setting
it to 40MB and 20MB respectively - both are a lot larger than the 1M
you were setting the dirty*bytes vm knobs to.

I've got a problematic server with 8GB RAM.  Even if set both to 1,
that's 80MB and the crappy disks I have in it will often only write
10-20MB/s or less due to the seekiness of the workload.  That means
delays of 5-10 seconds worst case which isn't fun.

-Dave
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