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), or is this a bug in kmem_cache_alloc_node_trace() itself? >>> And one more thing. Take a look at mempool, because it's generally used to solve the problem you have here >>> (guaranteed allocation in atomic context). >> As far as I understood the docs, mempools have a drawback of >> allocating too much memory which won't be available for any other use. > > As far as I understood your code, it has a drawback of > allocating too much memory which won't be available for any other use ;) > > However, now I think that mempool doesn't fit here. We never free > memory => never return it to pool. > And this will cause 5sec delays between allocation retries in mempool_alloc(). > > >> O'Reily's "Linux Device Drivers" even suggests not using mempools in >> any case when it's easier to deal with allocation failures (that >> advice is for device drivers, not sure if that stands for other >> subsystems though). >> >> >> -- >> Alexander Potapenko >> Software Engineer >> >> Google Germany GmbH >> Erika-Mann-Straße, 33 >> 80636 München >> >> Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle >> Registergericht und -nummer: Hamburg, HRB 86891 >> Sitz der Gesellschaft: Hamburg -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg -- 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