memory usage in P-1 stage 1

James Heinrich · 2005-03-19, 20:49

We all know the memory settings specified in Prime95 apply to P-1, stage2. However, it's not clear from the readme (or anywhere else) that memory usage may exceed those values, and exceed the default/oft-quoted "8MB" value. For example, running P-1 stage 1 of a top-range exponent (M79299821, in my case) uses about 90MB. LL testing seems to use about 45MB for the same exponent. I'm not sure how much memory trial factoring takes up.

I realize this is because of the abnormally-large exponents, but maybe the readme should mention this?

moo · 2005-03-19, 21:23

trial facting takes 1.4 megs of mem when prime95 is in taskbar mode.

ewmayer · 2005-03-22, 05:24

P-1 stage should need no more memory than an LL test.

James Heinrich · 2005-03-22, 18:26

Quote:

Originally Posted by ewmayer

P-1 stage should need no more memory than an LL test.

"should" and "does" don't seem to coincide in this case... P-1,stage1 takes twice the memory that the L-L of the exponent does.

ewmayer · 2005-03-22, 19:06

Quote:

Originally Posted by James Heinrich

"should" and "does" don't seem to coincide in this case... P-1,stage1 takes twice the memory that the L-L of the exponent does.

Hm, that almost sounds like stage 1 is using a right-to-left binary powering, which needs 2x the memory of a left-to-right, and roughly 50% more runtime. IMO the only reasons one would ever use right-to-left:

1) The product of all the stage 1 prime powers (needed by the LR powering) is too large to be easily computed/stored - but that needs a very large stage 1 bound;

2) If stage 2 fails to find a factor, one wants to go back and, starting with the original stage 1 residue, do a deeper stage 1 continuation.

George?

Prime95 · 2005-03-22, 20:05

Maybe we are confusing two terms. Prime95 is concerned with the working set, but perhaps James is reporting the total allocated memory.

P-1 allocates more memory than an LL test because it computes the left-to-right powering exponent. However, only one cache line of this memory will be in prime95's working set during stage 1 - so the two should have the same working set.

Otherwise, I'm at a loss to explain the difference.

2005-03-19, 20:49	#1
James Heinrich "James Heinrich" May 2004 ex-Northern Ontario 2·2,083 Posts	memory usage in P-1 stage 1 We all know the memory settings specified in Prime95 apply to P-1, stage2. However, it's not clear from the readme (or anywhere else) that memory usage may exceed those values, and exceed the default/oft-quoted "8MB" value. For example, running P-1 stage 1 of a top-range exponent (M79299821, in my case) uses about 90MB. LL testing seems to use about 45MB for the same exponent. I'm not sure how much memory trial factoring takes up. I realize this is because of the abnormally-large exponents, but maybe the readme should mention this?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Stage 2 Memory Setting - Again	Antonio	Software	6	2012-09-04 12:48
Stage 2 Memory Settings	gamer30	Software	17	2012-08-23 20:02
Memory usage during P-1 factoring	lidocorc	Software	2	2008-11-03 02:35
PauseWhileRunning & P-1 memory usage	James Heinrich	Software	4	2006-01-20 13:55
memory usage in stage 2 of P-1 factoring	gckw	Software	3	2003-09-07 06:56

2005-03-19, 21:23	#2
moo Jul 2004 Nowhere 1451₈ Posts	trial facting takes 1.4 megs of mem when prime95 is in taskbar mode.

2005-03-22, 05:24	#3
ewmayer ∂²ω=0 Sep 2002 República de California 5×2,351 Posts	P-1 stage should need no more memory than an LL test.

2005-03-22, 20:05	#6
Prime95 P90 years forever! Aug 2002 Yeehaw, FL 2×4,099 Posts	Maybe we are confusing two terms. Prime95 is concerned with the working set, but perhaps James is reporting the total allocated memory. P-1 allocates more memory than an LL test because it computes the left-to-right powering exponent. However, only one cache line of this memory will be in prime95's working set during stage 1 - so the two should have the same working set. Otherwise, I'm at a loss to explain the difference.