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. -- Michal Hocko SUSE Labs -- 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>