Re: less aggressive contigmalloc ?

On Fri, Aug 24, 2012 at 11:56:06AM -0500, Alan Cox wrote:
> On 08/24/2012 11:54, Luigi Rizzo wrote:
> >On Fri, Aug 24, 2012 at 11:12:51AM -0500, Alan Cox wrote:
> >>On 08/24/2012 09:57, Luigi Rizzo wrote:
> >>>On Fri, Aug 24, 2012 at 12:43:33AM -0500, Alan Cox wrote:
> >>>>On 08/23/2012 12:45, Luigi Rizzo wrote:
> >>>>>On Thu, Aug 23, 2012 at 12:08:40PM -0500, Alan Cox wrote:
> >>>>>...
> >>>>>>>yes i do see that.
> >>>>>>>
> >>>>>>>Maybe less aggressive with M_NOWAIT but still kills processes.
> >>>>>>Are you compiling world with MALLOC_PRODUCTION?  The latest version of
> >>>>>whatever the default is. But:
> >>>>>
> >>>>>>jemalloc uses significantly more memory when debugging options are
> >>>>>>enabled.  This first came up in a thread titled "10-CURRENT and swap
> >>>>>>usage" back in June.
> >>>>>>
> >>>>>>Even at its most aggressive, M_WAITOK, contigmalloc() does not 
> >>>>>>directly
> >>>>>>kill processes.  If process death coincides with the use of
> >>>>>>contigmalloc(), then it is simply the result of earlier, successful
> >>>>>>contigmalloc() calls, or for that matter any other physical memory
> >>>>>>allocation calls, having depleted the pool of free pages to the point
> >>>>>>that the page daemon runs and invokes vm_pageout_oom().
> >>>>>does it mean that those previous allocations relied on memory
> >>>>>overbooking ?
> >>>>Yes.
> >>>>
> >>>>>Is there a way to avoid that, then ?
> >>>>I believe that malloc()'s default minimum allocation size is 4MB.  You
> >>>>could reduce that.
> >>>>
> >>>>Alternatively, you can enable MALLOC_PRODUCTION.
> >>>i tried this, and as others mentioned it makes life
> >>>better and reduces the problem but contigmalloc still triggers
> >>>random process kills.
> >>I would be curious to see a stack backtrace when vm_pageout_oom() is 
> >>called.
> >you mean a backtrace of the process(es) that get killed ?
> 
> No, a backtrace showing who called vm_pageout_oom().  Simply add a 
> kdb_backtrace() call at the start of vm_pageout_oom().  There are two 
> possibilities.  I want to know which it is.

this is dmesg when I add kdb_backtrace()  at the start of vm_pageout_oom()
The '... netmap_finalize_obj_allocator... are from my calls to
contigmalloc, each one doing one-page allocations.
I get 7-8 'KDB: stack backtrace' blocks, then allocations
restart successfully, then more failures...
The reference to fork_exit() does not seem right, because i am
in a block where i call contigmalloc, so the caller of
vm_pageout_grow_cache() should be kmem_alloc_contig().

630.004926 netmap_finalize_obj_allocator [593] cluster at 8910 ok               
630.005563 netmap_finalize_obj_allocator [593] cluster at 8912 ok               
630.006077 netmap_finalize_obj_allocator [593] cluster at 8914 ok               
KDB: stack backtrace:                                                           
X_db_sym_numargs() at X_db_sym_numargs+0x1aa                                    
vm_pageout_oom() at vm_pageout_oom+0x19                                         
vm_pageout_grow_cache() at vm_pageout_grow_cache+0xd01                          
fork_exit() at fork_exit+0x11c                                                  
fork_trampoline() at fork_trampoline+0xe                                        
--- trap 0, rip = 0, rsp = 0xffffff8005f12cb0, rbp = 0 ---                      
KDB: stack backtrace:                                                           
X_db_sym_numargs() at X_db_sym_numargs+0x1aa                                    
vm_pageout_oom() at vm_pageout_oom+0x19                                         
vm_pageout_grow_cache() at vm_pageout_grow_cache+0xd01                          
fork_exit() at fork_exit+0x11c                                                  
fork_trampoline() at fork_trampoline+0xe                                        
--- trap 0, rip = 0, rsp = 0xffffff8005f12cb0, rbp = 0 ---                      
...

Some of the processes must be 'getty' because i also find
this line in dmesg:

<118>Aug 26 16:47:11 init: getty repeating too quickly on port /dev/ttyv7, sleep
ing 30 secs   

cheers
luigi