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Re: ext3 blocks other with large writes



On Thu, 2002-02-28 at 22:30, Andrew Morton wrote:

> There are a few things you can do:
> 
> You'll want
> http://www.zip.com.au/~akpm/linux/patches/2.4/2.4.18-rc1/make_request.patch
> to fix the elevator starvation problem.  This is officially in 2.4.19-pre1.
> 
> You'll want 
> http://www.zip.com.au/~akpm/linux/patches/2.4/2.4.18-pre9/read-latency2.patch
> which promotes reads ahead of writes.  Dunno if this will ever be
> merged, frankly.  It's a *fundamental* change to what is probably
> the single most important pieve of code in the kernel, from a performance
> point of view.
> 
> Now that's all well and good.  With these patches, reads should
> proceed nicely.  But if the process which is trying to read things
> accidentally does a write, it'll end up at the back of the
> queue, delayed for a long time.   You shuld prevent such accidents
> by mounting your filesystems with the `noatime' option.

I tried to apply the first patch to the RH kernel (first 2.4.9-21, which
is the one I'm running, and then 2.4.17-0.18 from rawhide, which
apparently is 2.4.18-rc1+rmap+O(1)+...), but they are significantly
different in blkdev.h and ll_rw_blk.c and I'm a bit wary that the
experience could turn bad (I would have to test on my work machine). So
I think I'll wait till the thing advances a bit more.

As for the 2nd patch I think it is a bit too radical for me... And the
caveat about mounting with noatime is quite awkward btw. Just out of
curiosity, wouldn't there a be way to avoid that kind of problem?

Thanks a lot for your help,

Diego

-- 
-------------------------------------------------------
Diego Santa Cruz
PhD. student
Publications available at http://ltswww.epfl.ch/~dsanta
Signal Processing Laboratory (LTS)
Swiss Federal Institute of Technology (EPFL)
EPFL - DE - LTS, CH-1015 Lausanne, Switzerland
E-mail:     Diego SantaCruz epfl ch
Phone:      +41 - 21 - 693 26 57
Fax:        +41 - 21 - 693 76 00
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