On 03/11/2016 02:18 PM, Alexander Potapenko wrote: > On Thu, Mar 10, 2016 at 5:58 PM, Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> wrote: >> 2016-03-08 14:42 GMT+03:00 Alexander Potapenko <glider@xxxxxxxxxx>: >>> On Tue, Mar 1, 2016 at 12:57 PM, Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> wrote: >>>>>> >>>>>>> + page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER); >>>>>> >>>>>> STACK_ALLOC_ORDER = 4 - that's a lot. Do you really need that much? >>>>> >>>>> Part of the issue the atomic context above. When we can't allocate >>>>> memory we still want to save the stack trace. When we have less than >>>>> STACK_ALLOC_ORDER memory, we try to preallocate another >>>>> STACK_ALLOC_ORDER in advance. So in the worst case, we have >>>>> STACK_ALLOC_ORDER memory and that should be enough to handle all >>>>> kmalloc/kfree in the atomic context. 1 page does not look enough. I >>>>> think Alex did some measuring of the failure race (when we are out of >>>>> memory and can't allocate more). >>>>> >>>> >>>> A lot of 4-order pages will lead to high fragmentation. You don't need physically contiguous memory here, >>>> so try to use vmalloc(). It is slower, but fragmentation won't be problem. >>> I've tried using vmalloc(), but turned out it's calling KASAN hooks >>> again. Dealing with reentrancy in this case sounds like an overkill. >> >> We'll have to deal with recursion eventually. Using stackdepot for >> page owner will cause recursion. >> >>> Given that we only require 9 Mb most of the time, is allocating >>> physical pages still a problem? >>> >> >> This is not about size, this about fragmentation. vmalloc allows to >> utilize available low-order pages, >> hence reduce the fragmentation. > I've attempted to add __vmalloc(STACK_ALLOC_SIZE, alloc_flags, > PAGE_KERNEL) (also tried vmalloc(STACK_ALLOC_SIZE)) instead of > page_alloc() and am now getting a crash in > kmem_cache_alloc_node_trace() in mm/slab.c, because it doesn't allow > the kmem_cache pointer to be NULL (it's dereferenced when calling > trace_kmalloc_node()). > > Steven, do you know if this because of my code violating some contract > (e.g. I'm calling vmalloc() too early, when kmalloc_caches[] haven't > been initialized), Probably. kmem_cache_init() goes before vmalloc_init(). > or is this a bug in kmem_cache_alloc_node_trace() > itself? > -- 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>