From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ua0-f198.google.com (mail-ua0-f198.google.com [209.85.217.198]) by kanga.kvack.org (Postfix) with ESMTP id 551A46B0279 for ; Tue, 30 May 2017 04:15:56 -0400 (EDT) Received: by mail-ua0-f198.google.com with SMTP id 50so22992753ual.5 for ; Tue, 30 May 2017 01:15:56 -0700 (PDT) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id i191sor1710977vkd.10.2017.05.30.01.15.55 for (Google Transport Security); Tue, 30 May 2017 01:15:55 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1131ff71-eb7a-8396-9a72-211f7077e5ec@arm.com> References: <1494897409-14408-1-git-send-email-iamjoonsoo.kim@lge.com> <20170516062318.GC16015@js1304-desktop> <20170524074539.GA9697@js1304-desktop> <20170525004104.GA21336@js1304-desktop> <1131ff71-eb7a-8396-9a72-211f7077e5ec@arm.com> From: Dmitry Vyukov Date: Tue, 30 May 2017 10:15:34 +0200 Message-ID: Subject: Re: [PATCH v1 00/11] mm/kasan: support per-page shadow memory to reduce memory consumption Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Murzin Cc: Joonsoo Kim , Andrew Morton , Andrey Ryabinin , Alexander Potapenko , kasan-dev , "linux-mm@kvack.org" , LKML , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , kernel-team@lge.com On Tue, May 30, 2017 at 9:58 AM, Vladimir Murzin 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@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org