On Tue, May 30, 2017 at 11:39 AM, Vladimir Murzin <vladimir.murzin@xxxxxxx> wrote: > > On 30/05/17 10:26, Dmitry Vyukov wrote: > > On Tue, May 30, 2017 at 11:08 AM, Vladimir Murzin > > <vladimir.murzin@xxxxxxx> wrote: > >>> <vladimir.murzin@xxxxxxx> wrote: > >>>> On 30/05/17 09:31, Vladimir Murzin wrote: > >>>>> [This sender failed our fraud detection checks and may not be who they appear to be. Learn about spoofing at http://aka.ms/LearnAboutSpoofing] > >>>>> > >>>>> On 30/05/17 09:15, Dmitry Vyukov wrote: > >>>>>> 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? > >>>>> > >>>>> page_ext is already here along with some other debug options ;) > >>> > >>> > >>> But page struct is also here. What am I missing? > >>> > >> > >> Probably, free room in page struct? I guess most of the page_ext stuff would > >> love to live in page struct, but... for instance, look at page idle tracking > >> which has to live in page_ext only for 32-bit. > > > > > > Sorry for my ignorance. What's the fundamental problem with just > > pushing everything into page struct? > > I think [1] has an answer for your question ;) It also has an answer for why we should put it into page struct :) > > > > > I don't see anything relevant in page struct comment. Nor I see "idle" > > nor "tracking" page struct. I see only 2 mentions of CONFIG_64BIT, but > > both declare the same fields just with different types (int vs short). > > Right, it is because implementation is based on page flags [1]: > > Note, since there is no room for extra page flags on 32 bit, this feature > uses extended page flags when compiled on 32 bit. > > > [1] https://lwn.net/Articles/565097/ > [2] 33c3fc7 ("mm: introduce idle page tracking") -- 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>
