Messages in this thread | | | Date | Wed, 24 Nov 2004 16:52:26 +0100 | From | Martin MOKREJŠ <> | Subject | Re: [PATCH] fix spurious OOM kills |
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Thomas Gleixner wrote: > On Tue, 2004-11-23 at 08:41 +0100, Martin MOKREJŠ wrote: > >>>One big problem when killing the requesting process or just sending >>>ENOMEM to the requesting process is, that exactly this process might be >>>a ssh login, when you try to log into to machine after some application >>>went crazy and ate up most of the memory. The result is that you >>>_cannot_ log into the machine, because the login is either killed or >>>cannot start because it receives ENOMEM. >> >>I believe the application is _first_ who will get ENOMEM. It must be >>terrible luck that it would ask exactly for the size of remaining free >>memory. Most probably, it will ask for less or more. "Less" in not >>a problem in this case, so consider it asks for more. Then, OOM killer >>might well expect the application asking for memory is most probably >>exactly the application which caused the trouble. > > > For one application, which eats up all memory the 2.4 ENOMEM bahviour > works. > > The scenario which made one of my boxes unusable under 2.4 is a forking > server, which gets out of control. The last fork gets ENOMEM and does > not happen, but the other forked processes are still there and consuming > memory. The server application does the correct thing. It receives > ENOMEM on fork() and cancels the connection request. On the next request > the game starts again. Somebody notices that the box is not repsonding > anymore and tries to login via ssh. Guess what happens. ssh login cannot > fork due to ENOMEM. The same will happen on 2.6 if we make it behave > like 2.4. > > We have TWO problems in oom handling: > > 1. When do we trigger the out of memory killer > > As far as my test cases go, 2.6.10-rc2-mm3 does not longer trigger the > oom without reason. > > 2. Which process do we select to kill > > The decision is screwed since the oom killer was introduced. Also the > reentrancy problem and some of the mechanisms in the out_of_memory > function have to be modified to make it work. > That's what my patch is addressing. > > >>>Putting hard coded decisions like "prefer sshd, xyz,...", " don't kill >>>a, b, c" are out of discussion. >> >>I'd go for it at least nowadays. > > > Sure, you can do so on your box, but can you accept, that we _CANNOT_ > hard code a list of do not kill apps, except init, into the kernel. I > don't want to see the mail thread on LKML, where the list of precious > application is discussed. > > >>> >>>The ideas which were proposed to have a possibility to set a "don't kill >>>me" or "yes, I'm a candidate" flag are likely to be a future way to go. >>>But at the moment we have no way to make this work in current userlands. >> >>Do you think login or sshd will ever use flag "yes, I'm a candidate"? >>I think exactly same bahaviour we get right now with those hard coded decisions >>you mention above. Otherwise the hard coded decision is programmed into >>every sshd, init instance anyway. I think it's not necessary to put >>login and shells on thsi ban list, user will re-login again. ;) > > > Having a generic interface to make this configurable is the only way to > go. So users can decide what is important in their environment. There is > more than a desktop PC environment and a lot of embedded boxes need to > protect special applications. > > >>>I refined the decision, so it does not longer kill the parent, if there >>>were forked child processes available to kill. So it now should keep >>>your bash alive. >> >>Yes, it doesn't kill parent bash. I don't understand the _doubled_ output >>in syslog, but maybe you do. Is that related to hyperthreading? ;) >>Tested on 2.6.10-rc2-mm2. > > >>oom-killer: gfp_mask=0xd2 >>Free pages: 3924kB (112kB HighMem) > > >>oom-killer: gfp_mask=0x1d2 >>Free pages: 3924kB (112kB HighMem) > > > No, it's not related to hyperthreading. It's on the way out. > > I put an additional check into the page allocator. Does this help ?
The application got killed. But, consider yourself the stacktrace ... ;) oom-killer: gfp_mask=0x1d2 DMA per-cpu: cpu 0 hot: low 2, high 6, batch 1 cpu 0 cold: low 0, high 2, batch 1 Normal per-cpu: cpu 0 hot: low 32, high 96, batch 16 cpu 0 cold: low 0, high 32, batch 16 HighMem per-cpu: cpu 0 hot: low 14, high 42, batch 7 cpu 0 cold: low 0, high 14, batch 7
Free pages: 3932kB (112kB HighMem) Active:128331 inactive:125322 dirty:0 writeback:0 unstable:0 free:983 slab:1941 mapped:253443 pagetables:794 DMA free:68kB min:68kB low:84kB high:100kB active:5444kB inactive:5304kB present:16384kB pages_scanned:11374 all_unreclaimable? yes protections[]: 0 0 0 Normal free:3752kB min:3756kB low:4692kB high:5632kB active:442984kB inactive:431092kB present:901120kB pages_scanned:936308 all_unreclaimable? yes protections[]: 0 0 0 HighMem free:112kB min:128kB low:160kB high:192kB active:64896kB inactive:64892kB present:131044kB pages_scanned:134868 all_unreclaimable? yes protections[]: 0 0 0 DMA: 1*4kB 0*8kB 0*16kB 0*32kB 1*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 68kB Normal: 0*4kB 1*8kB 0*16kB 1*32kB 0*64kB 1*128kB 0*256kB 1*512kB 1*1024kB 1*2048kB 0*4096kB = 3752kB HighMem: 0*4kB 0*8kB 1*16kB 1*32kB 1*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 112kB Swap cache: add 293335, delete 293335, find 44/60, race 0+0 [<c0103dfd>] dump_stack+0x1e/0x22 [<c013ec1c>] out_of_memory+0x97/0xcf [<c0146dc8>] try_to_free_pages+0x163/0x184 [<c013fde2>] __alloc_pages+0x27e/0x400 [<c0142368>] do_page_cache_readahead+0x15b/0x1b9 [<c013c5aa>] filemap_nopage+0x2d4/0x375 [<c014aa82>] do_no_page+0xc4/0x38c [<c014af30>] handle_mm_fault+0xde/0x189 [<c01166d5>] do_page_fault+0x456/0x6ad [<c0103a43>] error_code+0x2b/0x30 Out of Memory: Killed process 6672 (RNAsubopt). RNAsubopt: page allocation failure. order:0, mode:0x1d2 [<c0103dfd>] dump_stack+0x1e/0x22 [<c013fd90>] __alloc_pages+0x22c/0x400 [<c0142368>] do_page_cache_readahead+0x15b/0x1b9 [<c013c5aa>] filemap_nopage+0x2d4/0x375 [<c014aa82>] do_no_page+0xc4/0x38c [<c014af30>] handle_mm_fault+0xde/0x189 [<c01166d5>] do_page_fault+0x456/0x6ad [<c0103a43>] error_code+0x2b/0x30
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