Subject: Re: order 7 allocations from xt_recent

From: Reindl Harald <[email-masked]>
Date: Thu, 03 Jan 2013 20:51:22 +0100

Am 03.01.2013 19:00, schrieb Eric Dumazet:
> On Thu, 2013-01-03 at 12:26 -0500, Dave Jones wrote:
>> On Thu, Jan 03, 2013 at 12:11:15PM -0500, Dave Jones wrote:
>>  > On Thu, Jan 03, 2013 at 08:55:04AM -0800, Eric Dumazet wrote:
>>  >  > On Thu, 2013-01-03 at 11:43 -0500, Dave Jones wrote:
>>  >  > > We had a report from a user that shows this code trying
>>  >  > > to do enormous allocations, which isn't going to work too well..
>>  >  > >  ...
>>  >  > > Which is initialised thus..
>>  >  > > 
>>  >  > >         ip_list_hash_size = 1 << fls(ip_list_tot);
>>  >  > > 
>>  >  > > And ip_list_tot is 10000 in this case. Hmm ?
>>  >  > > 
>>  >  > > Complete report and setup described in his bug report at https://bugzilla.redhat.com/show_bug.cgi?id=890715
>>  >  > 
>>  >  > Yes, we had a report and a patch :
>>  >  > 
>>  >  > http://comments.gmane.org/gmane.linux.network/248216
>>  >  > 
>>  >  > I'll send it in a more formal way.
>>  > 
>>  > Ah! Excellent.
>>  > 
>>  > That 'check size and vmalloc/kmalloc accordingly' thing seems to be a pattern
>>  > that comes up time and time again.  Is it worth maybe making a more generic
>>  > version of that instead of open-coding it each time it comes up ?
>>
>> Something else that I'm puzzled by.
>>
>> In the report above, it failed to allocate 512kb, but..
>>
>> Node 0 Normal: 2388*4kB 347*8kB 1029*16kB 3512*32kB 29*64kB 2*128kB 1*256kB 5*512kB 1*1024kB 0*2048kB 0*4096kB = 147128kB
>>                                                                             ^^^^^^^^^^^^^^^^
>>
>> Shouldn't the allocator have been able to satisfy that anyway ?
>>
> 
> Might be something related to the CONFIG_COMPACTION=y and lumpy reclaim
> removal ?
> 
> Anyway, we keep a fraction of memory for ATOMIC allocations

on the machine there is even "vm.min_free_kbytes" set to 128 MB
however, something goes terrible wrong if cache-pages leads to
stack-traces about failed memory allocation

vm.swappiness = 0
vm.overcommit_memory = 1
vm.overcommit_ratio = 60
vm.vfs_cache_pressure = 30
vm.dirty_background_ratio = 15
vm.dirty_ratio = 40
vm.dirty_expire_centisecs = 1500
vm.dirty_writeback_centisecs = 1500
vm.zone_reclaim_mode = 0
vm.min_free_kbytes = 131072