Le 30/08/2016 à 19:06, William Stein a écrit : > On Tue, Aug 30, 2016 at 9:56 AM, Thierry Dumont > <tdum...@math.univ-lyon1.fr> wrote: >> I have two computers, and sage installed on both: >> >> 1) Ubuntu 12.04 , sage-7.3 on an nfs mount,y >> >> 2) Ubuntu 16.04, sage-7.3 on a local system, on a ssd. >> >> With the first one, sage starts slowly (as could be expected!), and I >> have time to look at sage starting with "top". And during the starting >> phase, before the prompt, sage uses more than 16 GB of virtual memory >> (VIRT: 16.380g); the same quantity is used when stopping sage (in the >> console interface). >> It seems quite large, no ? >> >> With the second machine, it's more difficult to see what happens with >> top, but it does not seems to use more than 7gb. >> >> Why such a large amount of memory ? (ok, it's virtual, but it's large, >> no ?). > > I think this is a hack that is used by PARI/GP, due to their > "interesting" primitive (but fast!) memory design. > > -- William > >> >> t.d. >>
Mhhh, yes.And they certainly do something with what they allocate; I
tried this (c++):
-------------------------------
#define DO_SOMETHING
int main()
{
//allocate a 16 gb array.
const long int n=2*1000000000;
long int *x=new long int[n];
#ifdef DO_SOMETHING
for(long int i=0;i<n;i++)
x[i]=0;
#endif
}
------------------------------
With DO_SOMETHING defined, time ./a.out:
real 0m7.352s
user 0m2.611s
sys 0m4.648s
and DO_SOMETHING undefined (as just allocating has quite no cost):
real 0m0.004s
user 0m0.004s
sys 0m0.000s
t.
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<<attachment: tdumont.vcf>>
