Hello David,
> > cat /proc/<pid>/pagemap
> >
> > and
> >
> > cat /proc/<pid>/task/<pid>/pagemap
> >
> > eats up to 100% of CPU while looping forever somewhere. On the other
> > hand on my old x86 the same commands take well below 1s so I
> > guess that is the expected behaviour.
>
> The patch below will speed this up for 32-bit processes but for 64-bit
> ones it's still going to take a long time.
>
> Cat'ing this file writes a 64-bit value for every possible page in the
> task's address space, which for 64-bit is an enormous number of
> entries.
>
> This is not how this file is supposed to be used. Programs are
> supposed to inspect /proc/${PID}/maps, and use those ranges to lseek()
> around the pagemap file and fish out the values they need.
I see. Sorry for the noise then 8-) I've got a couple of scripts for testing
/proc and /sys and I just noticed that some of processes started by them
would run for a couple hours eating 100% CPU which doesn't happen on other
arch'es I have around - hence my report. Thanks for clarification.
> This expensive operation is quite harmless, the process can still be
> killed, it is not unstoppable.
That's true.
> commit c101b088ba0ed16d7109b2f3c2d16798d162a535
> Author: David S. Miller <davem@xxxxxxxxxxxxx>
> Date: Wed Mar 26 17:32:33 2008 -0700
>
> [SPARC64]: Define TASK_SIZE_OF()
>
> This make "cat /proc/${PID}/pagemap" more efficient for
> 32-bit tasks.
This patch certainly helps in my case. Tested here:
sparc64 # time cat /proc/1/pagemap > /dev/null
real 0m0.046s
user 0m0.000s
sys 0m0.047s
Thanks,
Mariusz
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