On Tue, May 30, 2017 at 9:58 AM, Vladimir Murzin <vladimir.murzin@xxxxxxx> wrote: > On 29/05/17 16:29, Dmitry Vyukov wrote: >> I have an alternative proposal. It should be conceptually simpler and >> also less arch-dependent. But I don't know if I miss something >> important that will render it non working. >> Namely, we add a pointer to shadow to the page struct. Then, create a >> slab allocator for 512B shadow blocks. Then, attach/detach these >> shadow blocks to page structs as necessary. It should lead to even >> smaller memory consumption because we won't need a whole shadow page >> when only 1 out of 8 corresponding kernel pages are used (we will need >> just a single 512B block). I guess with some fragmentation we need >> lots of excessive shadow with the current proposed patch. >> This does not depend on TLB in any way and does not require hooking >> into buddy allocator. >> The main downside is that we will need to be careful to not assume >> that shadow is continuous. In particular this means that this mode >> will work only with outline instrumentation and will need some ifdefs. >> Also it will be slower due to the additional indirection when >> accessing shadow, but that's meant as "small but slow" mode as far as >> I understand. >> >> But the main win as I see it is that that's basically complete support >> for 32-bit arches. People do ask about arm32 support: >> https://groups.google.com/d/msg/kasan-dev/Sk6BsSPMRRc/Gqh4oD_wAAAJ >> https://groups.google.com/d/msg/kasan-dev/B22vOFp-QWg/EVJPbrsgAgAJ >> and probably mips32 is relevant as well. >> Such mode does not require a huge continuous address space range, has >> minimal memory consumption and requires minimal arch-dependent code. >> Works only with outline instrumentation, but I think that's a >> reasonable compromise. > > .. or you can just keep shadow in page extension. It was suggested back in > 2015 [1], but seems that lack of stack instrumentation was "no-way"... > > [1] https://lkml.org/lkml/2015/8/24/573 Right. It describes basically the same idea. How is page_ext better than adding data page struct? It seems that memory for all page_ext is preallocated along with page structs; but just the lookup is slower. -- 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>
