[Haskell-cafe] How to optimize a directory scanning?

Magicloud Magiclouds magicloud.magiclouds at gmail.com
Sun May 12 07:25:53 UTC 2019

Thanks for all replies. I did not track forks with strace since "I do
not have such code" although stack has threaded and rtsopts set. But
now `strace -f` clearly shows that there are qutie a lot of forking
for my code. Removing those options got me a 3% CPU usage reducing.
And as Neil said, ioctl or other syscalls in the whole reading
process, Haskell is more optimized than Rust.

I am trying posix-paths now.

Sorry, that was a part missing in sample code. isMyPid should be
called before reading the stat file.

@Brandon, @Joachim, @KC,
At least for me, how data is stored on disk is not related. /proc is a
virtual filesystem which just a kernel data structures exposed via IO

On Sun, May 12, 2019 at 2:27 PM Joachim Durchholz <jo at durchholz.org> wrote:
> Am 12.05.19 um 00:23 schrieb KC:
> > Are directories stored in consecutive disk blocks?
> That's something that you have to rely on the file system to organize
> for you.
> Brandon's answer is the traditional one for Unix filesystems, up to and
> including ext3fs. Modern filesystems try to do better (and often do),
> since scanning large directories has turned out to be so important.
> If you do performance testing, both bad and good filesystem performance
> may be accidental; if you want to know not just the typical behaviour
> but also the pathological cases, you'll either have to wait for user
> reports to come in or talk to real filesystem experts (and even their
> answers will mostly be on an "it depends" basis).
> Note that fragmentation is irrelevant for SSDs.
> The OP is at the "what system calls are being done" stage; optimization
> questions about fragmentation aren't going to be relevant to him I think.
> TL;DR: Don't worry about fragmentation, unless you are willing to spend
> a really high amount of time on detail optimization.
> Regards,
> Jo
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