[Linux-ia64] munmap() slowness

[Linux-ia64] munmap() slowness

[Andy Isaacson]

munmap on a 15TB anonymous area is extremely slow on our Itanium 2 box.

#include <sys/mman.h>
int main(void) {
    size_t s = 1024*1024*1024*1024L * 15;
    munmap(mmap(0, s, PROT_READ|PROT_WRITE,
                MAP_NORESERVE|MAP_PRIVATE|MAP_ANONYMOUS, -1, 0),
           s);
    return 0;
}

./a.out 0.00s user 1.51s system 100% cpu 1.515 total

The kernel is 2.4.19 plus linux-2.4.19-ia64-020821.diff.gz (plus some
local changes that shouldn't be relevant).

Of course this isn't a real app, but I thought this was an interesting
result.

Please CC me on any replies, as I am not subscribed to the list.

-andy

Re: [Linux-ia64] munmap() slowness

[David Mosberger]

>>>>> On Wed, 5 Mar 2003 17:30:01 -0600, Andy Isaacson <adi@hexapodia.org> said:

  Andy> munmap on a 15TB anonymous area is extremely slow on our Itanium 2 box.
  Andy> #include <sys/mman.h>
  Andy> int main(void) {
  Andy> size_t s = 1024*1024*1024*1024L * 15;
  Andy> munmap(mmap(0, s, PROT_READ|PROT_WRITE,
  Andy> MAP_NORESERVE|MAP_PRIVATE|MAP_ANONYMOUS, -1, 0),
  Andy> s);
  Andy> return 0;
  Andy> }

  Andy> ./a.out 0.00s user 1.51s system 100% cpu 1.515 total

  Andy> The kernel is 2.4.19 plus linux-2.4.19-ia64-020821.diff.gz (plus some
  Andy> local changes that shouldn't be relevant).

  Andy> Of course this isn't a real app, but I thought this was an interesting
  Andy> result.

  Andy> Please CC me on any replies, as I am not subscribed to the list.

$ uname -r
2.4.19-mckinley-smp
$ /usr/bin/time ./a.out
0.00user 0.00system 0:00.00elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (44major+13minor)pagefaults 0swaps

strace output says:

mmap(NULL, 16492674416640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE, -1, 0) = 0x20000000002b4000
munmap(0x20000000002b4000, 16492674416640) = 0

Seems to perform just fine.

	--david

Re: [Linux-ia64] munmap() slowness

[Andy Isaacson]

On Wed, Mar 05, 2003 at 03:45:24PM -0800, David Mosberger wrote:
> Andy> munmap on a 15TB anonymous area is extremely slow on our Itanium 2 box.
> Andy> #include <sys/mman.h>
> Andy> int main(void) {
> Andy> size_t s = 1024*1024*1024*1024L * 15;
> Andy> munmap(mmap(0, s, PROT_READ|PROT_WRITE,
> Andy> MAP_NORESERVE|MAP_PRIVATE|MAP_ANONYMOUS, -1, 0),
> Andy> s);
> Andy> return 0;
> Andy> }
>
> Andy> ./a.out 0.00s user 1.51s system 100% cpu 1.515 total
>
> Andy> The kernel is 2.4.19 plus linux-2.4.19-ia64-020821.diff.gz (plus some
> Andy> local changes that shouldn't be relevant).
> 
> $ uname -r
> 2.4.19-mckinley-smp
> $ /usr/bin/time ./a.out
> 0.00user 0.00system 0:00.00elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k
> 0inputs+0outputs (44major+13minor)pagefaults 0swaps

My bad, it turns out I logged into a different machine which is running
2.4.18-e.12smp from some interim RHAS 2.1 release.  When I re-ran the
test on the correct 2.4.19 box, the performance is fine.

-andy