On Sun, Jul 31, 2016 at 10:30 PM, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote: > On Fri, Jul 29, 2016 at 12:47:38PM -0700, Andy Lutomirski wrote: >> ---------- Forwarded message ---------- >> From: "Joonsoo Kim" <iamjoonsoo.kim@xxxxxxx> >> Date: Jul 28, 2016 7:57 PM >> Subject: Re: [RFC] can we use vmalloc to alloc thread stack if compaction failed >> To: "Andy Lutomirski" <luto@xxxxxxxxxx> >> Cc: "Xishi Qiu" <qiuxishi@xxxxxxxxxx>, "Michal Hocko" >> <mhocko@xxxxxxxxxx>, "Tejun Heo" <tj@xxxxxxxxxx>, "Ingo Molnar" >> <mingo@xxxxxxxxxx>, "Peter Zijlstra" <peterz@xxxxxxxxxxxxx>, "LKML" >> <linux-kernel@xxxxxxxxxxxxxxx>, "Linux MM" <linux-mm@xxxxxxxxx>, >> "Yisheng Xie" <xieyisheng1@xxxxxxxxxx> >> >> > On Thu, Jul 28, 2016 at 08:07:51AM -0700, Andy Lutomirski wrote: >> > > On Thu, Jul 28, 2016 at 3:51 AM, Xishi Qiu <qiuxishi@xxxxxxxxxx> wrote: >> > > > On 2016/7/28 17:43, Michal Hocko wrote: >> > > > >> > > >> On Thu 28-07-16 16:45:06, Xishi Qiu wrote: >> > > >>> On 2016/7/28 15:58, Michal Hocko wrote: >> > > >>> >> > > >>>> On Thu 28-07-16 15:41:53, Xishi Qiu wrote: >> > > >>>>> On 2016/7/28 15:20, Michal Hocko wrote: >> > > >>>>> >> > > >>>>>> On Thu 28-07-16 15:08:26, Xishi Qiu wrote: >> > > >>>>>>> Usually THREAD_SIZE_ORDER is 2, it means we need to alloc 16kb continuous >> > > >>>>>>> physical memory during fork a new process. >> > > >>>>>>> >> > > >>>>>>> If the system's memory is very small, especially the smart phone, maybe there >> > > >>>>>>> is only 1G memory. So the free memory is very small and compaction is not >> > > >>>>>>> always success in slowpath(__alloc_pages_slowpath), then alloc thread stack >> > > >>>>>>> may be failed for memory fragment. >> > > >>>>>> >> > > >>>>>> Well, with the current implementation of the page allocator those >> > > >>>>>> requests will not fail in most cases. The oom killer would be invoked in >> > > >>>>>> order to free up some memory. >> > > >>>>>> >> > > >>>>> >> > > >>>>> Hi Michal, >> > > >>>>> >> > > >>>>> Yes, it success in most cases, but I did have seen this problem in some >> > > >>>>> stress-test. >> > > >>>>> >> > > >>>>> DMA free:470628kB, but alloc 2 order block failed during fork a new process. >> > > >>>>> There are so many memory fragments and the large block may be soon taken by >> > > >>>>> others after compact because of stress-test. >> > > >>>>> >> > > >>>>> --- dmesg messages --- >> > > >>>>> 07-13 08:41:51.341 <4>[309805.658142s][pid:1361,cpu5,sManagerService]sManagerService: page allocation failure: order:2, mode:0x2000d1 >> > > >>>> >> > > >>>> Yes but this is __GFP_DMA allocation. I guess you have already reported >> > > >>>> this failure and you've been told that this is quite unexpected for the >> > > >>>> kernel stack allocation. It is your out-of-tree patch which just makes >> > > >>>> things worse because DMA restricted allocations are considered "lowmem" >> > > >>>> and so they do not invoke OOM killer and do not retry like regular >> > > >>>> GFP_KERNEL allocations. >> > > >>> >> > > >>> Hi Michal, >> > > >>> >> > > >>> Yes, we add GFP_DMA, but I don't think this is the key for the problem. >> > > >> >> > > >> You are restricting the allocation request to a single zone which is >> > > >> definitely not good. Look at how many larger order pages are available >> > > >> in the Normal zone. >> > > >> >> > > >>> If we do oom-killer, maybe we will get a large block later, but there >> > > >>> is enough free memory before oom(although most of them are fragments). >> > > >> >> > > >> Killing a task is of course the last resort action. It would give you >> > > >> larger order blocks used for the victims thread. >> > > >> >> > > >>> I wonder if we can alloc success without kill any process in this situation. >> > > >> >> > > >> Sure it would be preferable to compact that memory but that might be >> > > >> hard with your restriction in place. Consider that DMA zone would tend >> > > >> to be less movable than normal zones as users would have to pin it for >> > > >> DMA. Your DMA is really large so this might turn out to just happen to >> > > >> work but note that the primary problem here is that you put a zone >> > > >> restriction for your allocations. >> > > >> >> > > >>> Maybe use vmalloc is a good way, but I don't know the influence. >> > > >> >> > > >> You can have a look at vmalloc patches posted by Andy. They are not that >> > > >> trivial. >> > > >> >> > > > >> > > > Hi Michal, >> > > > >> > > > Thank you for your comment, could you give me the link? >> > > > >> > > >> > > I've been keeping it mostly up to date in this branch: >> > > >> > > https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/log/?h=x86/vmap_stack >> > > >> > > It's currently out of sync due to a bunch of the patches being queued >> > > elsewhere for the merge window. >> > >> > Hello, Andy. >> > >> > I have some questions about it. >> > >> > IIUC, to turn on HAVE_ARCH_VMAP_STACK on different architecture, there >> > is nothing to be done in architecture side if the architecture doesn't >> > support lazily faults in top-level paging entries for the vmalloc >> > area. Is my understanding is correct? >> > >> >> There should be nothing fundamental that needs to be done. On the >> other hand, it might be good to make sure the arch code can print a >> clean stack trace on stack overflow. >> >> If it's helpful, I just pushed out anew > > You mean that you can turn on HAVE_ARCH_VMAP_STACK on the other arch? It > would be helpful. :) > >> >> > And, I'd like to know how you search problematic places using kernel >> > stack for DMA. >> > >> >> I did some searching for problematic sg_init_buf calls using >> Coccinelle. I'm not very good at Coccinelle, so I may have missed >> something. > > I'm also not familiar with Coccinelle. Could you share your .cocci > script? I can think of following one but there would be a better way. > > virtual report > > @stack_var depends on report@ > type T1; > expression E1, E2; > identifier I1; > @@ > ( > * T1 I1; > ) > ... > ( > * sg_init_one(E1, &I1, E2) > | > * sg_set_buf(E1, &I1, E2) > ) > > @stack_arr depends on report@ > type T1; > expression E1, E2, E3; > identifier I1; > @@ > ( > * T1 I1[E1]; > ) > ... > ( > * sg_init_one(E2, I1, E3) > | > * sg_set_buf(E2, I1, E3) > ) > > $ cat sgstack.cocci @@ local idexpression S; expression A, B; @@ ( * sg_init_one(A, &S, B) | * virt_to_phys(&S) not very inspiring. I barely understand Coccinelle syntax, and sadly I find the manual nearly incomprehensible. I can read the grammar, but that doesn't mean I know what the various declarations do. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>