[LTP] [PATCH] mem/lib: keep allocating memory until get an error in single process

[Li Wang <liwang@redhat.com>]

On Mon, Jun 20, 2016 at 06:43:18AM -0400, Jan Stancek wrote:
> 
> 
> ----- Original Message -----
> > From: "Li Wang" <liwang@redhat.com>
> > To: jstancek@redhat.com
> > Cc: ltp@lists.linux.it
> > Sent: Monday, 20 June, 2016 11:53:05 AM
> > Subject: [PATCH] mem/lib: keep allocating memory until get an error in single process
> > 
> > We occasionally catch errors like:
> > oom03       0  TINFO  :  start OOM testing for KSM pages.
> > oom03       0  TINFO  :  expected victim is 3490.
> > oom03       6  TFAIL  :  mem.c:163: victim unexpectedly ended with retcode:
> > 0, expected: 12
> > oom03       0  TINFO  :  set overcommit_memory to 0
> > 
> > It cames from the caller testoom(0, 1, ENOMEM, 1). The full reason is that
> > function child_alloc() go into single process mode, then successfully finish
> > the memory allocation and return 0.
> 
> Description above doesn't explain why you get 0, when oom03 is set to run
> in cgroup with memory.memsw.limit_in_bytes == TESTMEM, and then allocates
> TESTMEM + MB.
> 
> My guess is a KSM scan merged some pages before you have hit the limit.
That might be.

> Do yo get these failures always during KSM test?
No, I just get the failures only once during my test.

> > 
> > In this patch, let's make it (in single mode) keep allocating memory with
> > an incresed length in order to avoid 0 returned.

Hmm, now I think these codes have two problems.

1. As you said the KSM merge same pages and let the oom03 failed as above.


2. The child_alloc() probably should also do memory allocation with an infinite loop
in single process mode. Because if someone has a caller testoom(0, 1, ENOMEM, 1) at other
place in future, that'll be easily get fauilures.

e.g.  change the testoom(...) as 'testoom(0, 1, ENOMEM, 1)' in oom01.c,
it failed like that.

# ./oom01 
oom01       0  TINFO  :  set overcommit_memory to 2
oom01       0  TINFO  :  expected victim is 20068.
oom01       0  TINFO  :  thread (7f05a5051700), allocating 1074790400 bytes.
oom01       1  TFAIL  :  mem.c:165: victim unexpectedly ended with retcode: 0, expected: 12
oom01       0  TINFO  :  set overcommit_memory to 0
oom01       0  TINFO  :  expected victim is 20069.

Or, can we solve them in one method?

Li Wang