[arch-general] Limiting pacman's IO rate

Yannis Juglaret yjuglaret at gmail.com
Fri May 22 08:49:52 UTC 2015


Thanks for the hints! Solution #1 looks great. As for solution #2, I 
don't have any problem downloading the ghc package (which is "only" 71.7 
MB) but only installing it (which requires 738.2 MB), so my guess is 
that pacman -U would trigger the same problem, but mixing #1 and #2 
could be useful for bigger packages (if any).

However, I also have great news on my side. If I enable the "Use host IO 
caching" option, VirtualBox stops trying to manage the disk IO cache 
itself, and everything works just fine. So that's probably where the bug 
was located. Problem solved!

For the record, I have a guess regarding why my commands didn't seem to 
affect pacman: blkio will only limit direct IO rate, not cached IO, so 
unless the program you execute performs direct IO you can't notice the 


-- Yannis

Le 22/05/2015 09:38, Rodrigo Rivas a écrit :
> On Thu, May 21, 2015 at 3:58 PM, Yannis Juglaret <yjuglaret at gmail.com> wrote:
>> Dear archers,
>> Is there something wrong in the commands I have written above? Is there a
>> way to check that the limitation is indeed enforced? (maybe the source of
>> the bug is elsewhere) Alternatively, can you think of another solution to
>> this problem?
> No idea about your commands, but I have a few alternative solutions...
> let's see if any one works.
> Solution #1.
> 1. Run `pacman -S ghc` normally.
> 2. When it advances about 10%, hopefully without crashing, press
> Ctrl+Z to sleep the process.
> 3. Wait a bit until the cache memory stabilizes, then run `sync` to
> force the remaining cached data to disk.
> 4. Type `fg` to continue the instalation,
> 5. Go to step 2 and repeat until finished.
> Solution #2.
> 1. Run `pacman -S -p ghc`. That will dump the URL of the package but
> it will do nothing else.
> 2. In the host OS (Ubuntu) get the package with `wget <url>` or
> whatever download command you prefer.
> 3. Copy the just downloaded file to the guest OS (Arch). You can use
> rsync, in case the copy gets interrupted.
> 4. Install the program with `pacman -U <file>`.

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