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. 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). I wonder if we can alloc success without kill any process in this situation. Maybe use vmalloc is a good way, but I don't know the influence. 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>