On 30/05/17 10:45, Dmitry Vyukov wrote: > 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 :) Glad you find it useful ;) I'd be glad to see it lands into 32-bit world :) Cheers Vladimir > > >> >>> >>> 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>
