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? Thanks, Xishi Qiu -- 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>