Opened 9 years ago
Closed 6 years ago
#10262 closed enhancement (duplicate)
memory leak in scalar*vector multiplication
Reported by:  dimpase  Owned by:  jason, was 

Priority:  major  Milestone:  sageduplicate/invalid/wontfix 
Component:  linear algebra  Keywords:  linear algebra, memory leak 
Cc:  mderickx  Merged in:  
Authors:  Reviewers:  
Report Upstream:  N/A  Work issues:  
Branch:  Commit:  
Dependencies:  #13304  Stopgaps: 
Description
Here is an example
sage: for i in range(1,8): A=(1/2)*vector([x/2 for x in range(i*1000)]) get_memory_usage() ....: 921.53125 1287.4765625 2111.984375 3577.546875 5867.19140625 9164.109375 ... (killed, due to running out of memory)
The printed numbers in Mb. Needless to say:
sage: for i in range(1,8): ....: A=vector([x/2 for x in range(i*1000)]) ....: get_memory_usage() ....: 828.91015625 829.4453125 829.73046875 830.0 830.55859375 830.75 831.0078125
works as expected. (This is with Sage 4.6 on x64, but is not limited to this particular platform: see https://groups.google.com/group/sagedevel/browse_thread/thread/e86f13c78b92a8bb?hl=en. Sage 4.5.3 shows the same behaviour.)
Attachments (1)
Change History (20)
comment:1 Changed 9 years ago by
 Summary changed from memory leak in scalar*vector mutiplication to memory leak in scalar*vector multiplication
comment:2 Changed 9 years ago by
comment:3 followup: ↓ 4 Changed 9 years ago by
As I mentioned on the thread, I tracked this down to a call from the coercion system to create an element of the parent. The coercion system did this when it was trying to figure out the action of the number on the vector:
The problem seems to stem from the lines
cdef Element x = X.an_element() cdef Element y = Y.an_element()
inside of the detect_element_action
function in coerce_actions.pyx
. Notice:
sage: v=vector(range(10000)) sage: get_memory_usage() 206.84765625 sage: w=v.parent().an_element() sage: get_memory_usage() 3321.14453125
comment:4 in reply to: ↑ 3 ; followup: ↓ 12 Changed 9 years ago by
Replying to jason:
As I mentioned on the thread, I tracked this down to a call from the coercion system to create an element of the parent.
So w
is a 10000 long vector over "ambient_pid_with_category". I'd call this alone a bug, for this is horribly inefficient.
Coercion for module operation could be much better...
My guess is that "an_element()" gets memoised, and retained instead of being destroyed at each forloop. Indeed:
sage: for i in [1,2,3,4,1,2,3,4]: ....: ....: A=(1/2)*vector([x/2 for x in range(i*1000)]) ....: get_memory_usage() ....: 261.58984375 513.59765625 1073.109375 2057.37890625 2057.37890625 2057.37890625 2057.37890625 2057.62890625 sage: for i in [1,3,5,1,3,5]: A=(1/2)*vector([x/2 for x in range(i*1000)]) get_memory_usage() ....: 2057.62890625 2057.62890625 3614.55078125 3614.55078125 3614.80078125 3615.05078125
So we get these huge vectors clogging up the memory, in hope that someone might want to compute in the free modules (over ambient_pid_with_category) of these dimensions again...
Should one just turn the memoisation for modules off completely? This would not cure the coercion inefficiency completely, but at least would prevent this leak...
comment:5 followup: ↓ 6 Changed 9 years ago by
 Priority changed from blocker to major
Why is this a blocker?
comment:6 in reply to: ↑ 5 Changed 9 years ago by
 Type changed from defect to enhancement
Replying to jdemeyer:
Why is this a blocker?
it is not, indeed. After investigating what happens, I forgot to change it to major, sorry.
comment:7 Changed 9 years ago by
This might also be related to #10570 since that ticket shows that there are call stack frames in the coerce_actions framework which stay alive for some reason.
comment:8 Changed 9 years ago by
 Cc mderickx added
Changed 9 years ago by
comment:9 Changed 9 years ago by
sorry uploaded a patch to the wrong ticket
comment:10 Changed 6 years ago by
 Milestone changed from sage5.11 to sage5.12
comment:11 Changed 6 years ago by
 Milestone changed from sage6.1 to sage6.2
comment:12 in reply to: ↑ 4 Changed 6 years ago by
Replying to dimpase:
My guess is that "an_element()" gets memoised, and retained instead of being destroyed at each forloop.
At least with #14711, the parent and its cached elements appear to be correctly destroyed after each loop turn. However, calling an_element()
triggers the computation of a basis, and the whole basis is cached!
sage: for i in [4, 3, 2, 1, 4, 3, 2, 1]: del A; gc.collect(); A=(1/2)*vector([x/2 for x in range(i*1000)]); get_memory_usage() ....: 4029 2483.984375 4030 1842.5390625 3030 1831.33203125 2030 1831.33203125 1030 2483.984375 4030 1842.54296875 3030 1831.33203125 2030 1831.33203125
Possible quick fix, with some code duplication:

src/sage/modules/free_module.py
diff git a/src/sage/modules/free_module.py b/src/sage/modules/free_module.py index a61b433..81a626c 100644
a b class FreeModule_ambient(FreeModule_generic): 4409 4409 """ 4410 4410 return self 4411 4411 4412 def gen(self, i): 4413 if i < 0 or i >= self.rank(): 4414 raise ValueError, "Generator %s not defined."%i 4415 v = self.zero().__copy__() 4416 v[i] = self.base_ring()(1) 4417 v.set_immutable() 4418 return v 4419 4412 4420 def basis(self): 4413 4421 """ 4414 4422 Return a basis for this ambient free module.
But I am not convinced it is such a good idea in general to cache the basis of a FreeModule_ambient
...
comment:13 Changed 6 years ago by
Turns out there is already a more polished version of the fix I was suggesting at #13304.
comment:14 Changed 6 years ago by
 Milestone changed from sage6.2 to sageduplicate/invalid/wontfix
 Status changed from new to needs_review
comment:15 followup: ↓ 17 Changed 6 years ago by
 Dependencies set to 13304
 Status changed from needs_review to needs_info
perhaps this ticket should at least provide a doctest that this issue is fixed by #13304?
comment:16 Changed 6 years ago by
 Dependencies changed from 13304 to #13304
comment:17 in reply to: ↑ 15 Changed 6 years ago by
comment:18 Changed 6 years ago by
 Status changed from needs_info to positive_review
comment:19 Changed 6 years ago by
 Resolution set to duplicate
 Status changed from positive_review to closed
FWIW, I've found when building on Solaris with a special library for memory allocation, which allows leaks to be detected, before I got to the
there was already memory leaked. I think it was only 14 bytes, but once I did a few calculations, more showed up. I think there are quite a few in Sage. Of course, some are more serious than others, but whatever the amount of memory leaked, it shows there's a coding error.
Dave