Date: Wed, 30 Nov 2011 15:59:14 -0600 From: Alan Cox <alan.l.cox@gmail.com> To: Andreas Tobler <andreast-list@fgznet.ch> Cc: Kostik Belousov <kostikbel@gmail.com>, FreeBSD Arch <freebsd-arch@freebsd.org> Subject: Re: powerpc64 malloc limit? Message-ID: <CAJUyCcO%2B76VirEbArnRPKx8JVGRfy8mknN4A7p1XGnug=vo8yw@mail.gmail.com> In-Reply-To: <4ED6A36D.1050107@fgznet.ch> References: <4ED5BE19.70805@fgznet.ch> <20111130162236.GA50300@deviant.kiev.zoral.com.ua> <4ED65F70.7050700@fgznet.ch> <20111130170936.GB50300@deviant.kiev.zoral.com.ua> <4ED66B75.3060409@fgznet.ch> <20111130200103.GE50300@deviant.kiev.zoral.com.ua> <4ED698EB.8090904@fgznet.ch> <20111130212439.GF50300@deviant.kiev.zoral.com.ua> <4ED6A36D.1050107@fgznet.ch>
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On Wed, Nov 30, 2011 at 3:43 PM, Andreas Tobler <andreast-list@fgznet.ch>wrote: > On 30.11.11 22:24, Kostik Belousov wrote: > >> On Wed, Nov 30, 2011 at 09:58:19PM +0100, Andreas Tobler wrote: >> >>> On 30.11.11 21:01, Kostik Belousov wrote: >>> >>>> On Wed, Nov 30, 2011 at 06:44:21PM +0100, Andreas Tobler wrote: >>>> >>>>> On 30.11.11 18:09, Kostik Belousov wrote: >>>>> >>>>>> On Wed, Nov 30, 2011 at 05:53:04PM +0100, Andreas Tobler wrote: >>>>>> >>>>>>> On 30.11.11 17:22, Kostik Belousov wrote: >>>>>>> >>>>>>>> On Wed, Nov 30, 2011 at 06:24:41AM +0100, Andreas Tobler wrote: >>>>>>>> >>>>>>>>> All, >>>>>>>>> >>>>>>>>> while working on gcc I found a very strange situation which >>>>>>>>> renders my >>>>>>>>> powerpc64 machine unusable. >>>>>>>>> The test case below tries to allocate that much memory as 'wanted'. >>>>>>>>> The >>>>>>>>> same test case on amd64 returns w/o trying to allocate mem because >>>>>>>>> the >>>>>>>>> size is far to big. >>>>>>>>> >>>>>>>>> I couldn't find the reason so far, that's why I'm here. >>>>>>>>> >>>>>>>>> As Nathan pointed out the VM_MAXUSER_SIZE is the biggest on >>>>>>>>> powerpc64: >>>>>>>>> #define VM_MAXUSER_ADDRESS (0x7ffffffffffff000UL) >>>>>>>>> >>>>>>>>> So, I'd expect a system to return an allocation error when a user >>>>>>>>> tries >>>>>>>>> to allocate too much memory and not really trying it and going to >>>>>>>>> be >>>>>>>>> unusable. Iow, I'd exepect the situation on powerpc64 as I see on >>>>>>>>> amd64. >>>>>>>>> >>>>>>>>> Can anybody explain me the situation, why do I not have a working >>>>>>>>> limit >>>>>>>>> on powerpc64? >>>>>>>>> >>>>>>>>> The machine itself has 7GB RAM and 12GB swap. The amd64 where I >>>>>>>>> compared >>>>>>>>> has around 4GB/4GB RAM/swap. >>>>>>>>> >>>>>>>>> TIA, >>>>>>>>> Andreas >>>>>>>>> >>>>>>>>> include<stdlib.h> >>>>>>>>> #include<stdio.h> >>>>>>>>> >>>>>>>>> int main() >>>>>>>>> { >>>>>>>>> void *p; >>>>>>>>> >>>>>>>>> p = (void*) malloc (1152921504606846968ULL); >>>>>>>>> if (p != NULL) >>>>>>>>> printf("p = %p\n", p); >>>>>>>>> >>>>>>>>> printf("p = %p\n", p); >>>>>>>>> return (0); >>>>>>>>> } >>>>>>>>> >>>>>>>> >>>>>>>> First, you should provide details of what consistutes 'the unusable >>>>>>>> machine situation' on powerpc. >>>>>>>> >>>>>>> >>>>>>> I can not login anymore, everything is stuck except the core control >>>>>>> mechanisms for example the fan controller. >>>>>>> >>>>>>> Top reports 'ugly' figures, below from a earlier try: >>>>>>> >>>>>>> last pid: 6790; load averages: 0.78, 0.84, 0.86 up 0+00:34:52 >>>>>>> 22:42:29 47 processes: 1 running, 46 sleeping >>>>>>> CPU: 0.0% user, 0.0% nice, 15.4% system, 11.8% interrupt, 72.8% >>>>>>> idle >>>>>>> Mem: 5912M Active, 570M Inact, 280M Wired, 26M Cache, 104M Buf, 352K >>>>>>> Free >>>>>>> Swap: 12G Total, 9904M Used, 2383M Free, 80% Inuse, 178M Out >>>>>>> >>>>>>> PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU >>>>>>> COMMAND >>>>>>> 6768 andreast 1 52 01073741824G 6479M pfault 1 0:58 >>>>>>> 18.90% 31370. >>>>>>> >>>>>>> And after my mem and swap are full I see swap_pager_getswapspace(16) >>>>>>> failed. >>>>>>> >>>>>>> In this state I can only power-cycle the machine. >>>>>>> >>>>>>> That said, on amd64 the user map is between 0 and 0x7fffffffffff, >>>>>>>> which >>>>>>>> obviously less then the requested allocation size 0x100000000000000. >>>>>>>> If you look at the kdump output on amd64, you will see that malloc() >>>>>>>> tries to mmap() the area, fails and retries with obreak(). Default >>>>>>>> virtual memory limit is unlimited, so my best quess is that on amd64 >>>>>>>> vm_map_findspace() returns immediately. >>>>>>>> >>>>>>>> On powerpc64, I see no reason why vm_map_entry cannot be allocated, >>>>>>>> but >>>>>>>> please note that vm object and pages shall be only allocated on >>>>>>>> demand. >>>>>>>> So I am curious how does your machine breaks and where. >>>>>>>> >>>>>>> >>>>>>> I would expect that the 'system' does not allow me to allocate that >>>>>>> much >>>>>>> of ram. >>>>>>> >>>>>> >>>>>> Does the issue with machine going into limbo reproducable with the >>>>>> code >>>>>> you posted ? >>>>>> >>>>> >>>>> If I understand you correctly, yes. I can launch the test case and the >>>>> machine is immediately unusable. Means I can not kill the process nor >>>>> can I log in. Also, top does not show anything useful. >>>>> >>>> Again, let me restate my question: the single mmap() of the huge size is >>>> enough for powerpc64 machine to break apart ? >>>> >>> >>> I can't answer. I don't know yet. >>> >>> What happen if you insert sleep(1000000); call before return ? Do not >>>> kill >>>> the process, I want to know is machine dead while the process sleeps. >>>> >>> >>> Ok, during the 'sleep' the machine is usable. top is reporting figures, >>> I can log in and edit files. The process runs now for aboutt 30'. >>> >>> When I kill the process, I do not get back to the shell nor can I log >>> in. Also top stops reporting. >>> But as you said, I didn't kill in this run. >>> >> Then, as Alan Cox pointed out, caused by the approach taken in powerpc64 >> pmap to handle pmap_remove(). It is definitely arch-specific. >> > > Ok. I think you mean moea64_remove which is pmap_remove, right? > > Where did Alan pointed this out? > > I was in a rush earlier, so I sent a short, cryptic note to Kostik privately. Alan
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