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. -- 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>