On 05/16/2017 04:16 AM, js1...@gmail.com wrote: > From: Joonsoo Kim <iamjoonsoo....@lge.com> > > Hello, all. > > This is an attempt to recude memory consumption of KASAN. Please see > following description to get the more information. > > 1. What is per-page shadow memory > > This patch introduces infrastructure to support per-page shadow memory. > Per-page shadow memory is the same with original shadow memory except > the granualarity. It's one byte shows the shadow value for the page. > The purpose of introducing this new shadow memory is to save memory > consumption. > > 2. Problem of current approach > > Until now, KASAN needs shadow memory for all the range of the memory > so the amount of statically allocated memory is so large. It causes > the problem that KASAN cannot run on the system with hard memory > constraint. Even if KASAN can run, large memory consumption due to > KASAN changes behaviour of the workload so we cannot validate > the moment that we want to check. > > 3. How does this patch fix the problem > > This patch tries to fix the problem by reducing memory consumption for > the shadow memory. There are two observations. >
I think that the best way to deal with your problem is to increase shadow scale size. You'll need to add tunable to gcc to control shadow size. I expect that gcc has some places where 8-shadow scale size is hardcoded, but it should be fixable. The kernel also have some small amount of code written with KASAN_SHADOW_SCALE_SIZE == 8 in mind, which should be easy to fix. Note that bigger shadow scale size requires bigger alignment of allocated memory and variables. However, according to comments in gcc/asan.c gcc already aligns stack and global variables and at 32-bytes boundary. So we could bump shadow scale up to 32 without increasing current stack consumption. On a small machine (1Gb) 1/32 of shadow is just 32Mb which is comparable to yours 30Mb, but I expect it to be much faster. More importantly, this will require only small amount of simple changes in code, which will be a *lot* more easier to maintain. I'd start from implementing this on the kernel side only. With KASAN_OUTLINE and disabled stack instrumentation (--param asan-stack=0) it's doable without any changes in gcc. ... > base vs patched > > MemTotal: 858 MB vs 987 MB > runtime: 0 MB vs 30MB > Net Available: 858 MB vs 957 MB > > For 4096 MB QEMU system > > MemTotal: 3477 MB vs 4000 MB > runtime: 0 MB vs 50MB > > base vs patched (2048 MB QEMU system) > 204 s vs 224 s > Net Available: 3477 MB vs 3950 MB > > Thanks.
